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# 16 The emulator file formats

This chapter gives a technical description of the various files supported by the emulators.

## 16.1 The T64 tape image format

(This section was taken from the C64S distribution.)

The `T64` File Structure was developed by Miha Peternel for use in the C64S emulator. It is easy to use and allows future extensions.

### 16.1.1 T64 File structure

Offset | Size | Description
0 | 64 | tape record
64 | 32*n | file records for n directory entries
64+32*n | varies | binary contents of the files

### 16.1.2 Tape Record

Offset | Size | Description
0 | 32 | DOS tape description + EOF (for type)
32 | 2 | tape version ($0200)
34 | 2 | number of directory entries
36 | 2 | number of used entries (can be 0 in my loader)
38 | 2 | free
40 | 24 | user description as displayed in tape menu

### 16.1.3 File record

Offset | Size | Description
0 | 1 | entry type (see below)
1 | 1 | C64 file type
2 | 2 | start address
4 | 2 | end address
6 | 2 | free
8 | 4 | offset of file contents start within T64 file
12 | 4 | free
16 | 16 | C64 file name

Valid entry types are:

Code | Explanation
`0` | free entry
`1` | normal tape file
`2` | tape file with header: header is saved just before file data
`3` | memory snapshot v0.9, uncompressed
`4` | tape block
`5` | digitized stream
`6` ... `255` | reserved

Notes:

- VICE only supports file type `1`.
- Types `3`, `4` and `5` are subject to change (and are rarely used).

## 16.2 The G64 GCR-encoded disk image format

(This section was contributed by Peter Schepers and slightly edited by Ettore Perazzoli.)

This format was defined in 1998 as a cooperative effort between several emulator people, mainly Per Håkan Sundell, author of the CCS64 C64 emulator, Andreas Boose of the VICE CBM emulator team and Joe Forster/STA, the author of Star Commander. It was the first real public attempt to create a format for the emulator community which removed almost all of the drawbacks of the other existing image formats, namely `D64`.

The intention behind `G64` is not to replace the widely used `D64` format, as `D64` works fine with the vast majority of disks in existence. It is intended for those small percentage of programs which demand to work with the 1541 drive in a non-standard way, such as reading or writing data in a custom format. The best example is with speeder software such as Action Cartridge in Warp Save mode or Vorpal which write track/sector data in another format other than standard GCR. The other obvious example is copy-protected software which looks for some specific data on a track, like the disk ID, which is not stored in a standard `D64` image.

`G64` has a deceptively simply layout for what it is capable of doing. We have a signature, version byte, some predefined size values, and a series of offsets to the track data and speed zones. It is what's contained in the track data areas and speed zones which is really at the heart of this format.

Each track entry in simply the raw stream of GCR data, just what a read head would see when a diskette is rotating past it. How the data gets interpreted is up to the program trying to access the disk. Because the data is stored in such a low-level manner, just about anything can be done. Most of the time I would suspect the data in the track would be standard sectors, with SYNC, GAP, header, data and checksums. The arrangement of the data when it is in a standard GCR sector layout is beyond the scope of this document.

Since it is a flexible format in both track count and track byte size, there is no "standard" file size. However, given a few constants like 42 tracks and halftracks, a track size of 7928 bytes and no speed offset entries, the typical file size will a minimum of 333744 bytes.

Below is a dump of the header, broken down into its various parts. After that will be an explanation of the track offset and speed zone offset areas, as they demand much more explanation.

    Addr  00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
    ----  -----------------------------------------------
    0000: 47 43 52 2D 31 35 34 31 00 54 F8 1E .. .. .. ..

Offset | Description
$0000-0007 | File signature (`GCR-1541`)
$0008 | `G64` version (presently only $00 defined)
$0009 | Number of tracks in image (usually $54, decimal 84)
$000A-000B | Size of each stored track in bytes (usually 7928, or $1EF8) in LO/HI format.

An obvious question here is "why are there 84 tracks defined when a normal `D64` disk only has 35 tracks?" Well, by definition, this image includes all half-tracks, so there are actually 42 tracks and 42 half tracks. The 1541 stepper motor can access up to 42 tracks and the in-between half-tracks. Even though using more than 35 tracks is not typical, it was important to define this format from the start with what the 1541 is capable of doing, and not just what it typically does.

At first, the defined track size value of 7928 bytes may seem to be arbitrary, but it is not. It is determined by the fastest write speed possible (speed zone 0), coupled with the average rotation speed of the disk (300 rpm). After some math, the answer that actually comes up is 7692 bytes. Why the discrepency between the actual size of 7692 and the defined size of 7928? Simply put, not all drives rotate at 300 rpm. Some can be faster or slower, so a upper safety margin of +3% was built added, in case some disks rotate slower and can write more data. After applying this safety factor, and some rounding-up, 7928 bytes per track was arrived at.

Also note that this upper limit of 7928 bytes per track really only applies to 1541 and compatible disks. If this format were applied to another disk type like the SFD1001, this value would be higher.

Below is a dump of the first section of a `G64` file, showing the offsets to the data portion for each track and half-track entry. Following that is a dump of the speed zone offsets.

    Addr  00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
    ----  -----------------------------------------------
    0000: .. .. .. .. .. .. .. .. .. .. .. .. AC 02 00 00
    0010: 00 00 00 00 A6 21 00 00 00 00 00 00 A0 40 00 00
    0020: 00 00 00 00 9A 5F 00 00 00 00 00 00 94 7E 00 00
    0030: 00 00 00 00 8E 9D 00 00 00 00 00 00 88 BC 00 00
    0040: 00 00 00 00 82 DB 00 00 00 00 00 00 7C FA 00 00
    0050: 00 00 00 00 76 19 01 00 00 00 00 00 70 38 01 00
    0060: 00 00 00 00 6A 57 01 00 00 00 00 00 64 76 01 00
    0070: 00 00 00 00 5E 95 01 00 00 00 00 00 58 B4 01 00
    0080: 00 00 00 00 52 D3 01 00 00 00 00 00 4C F2 01 00
    0090: 00 00 00 00 46 11 02 00 00 00 00 00 40 30 02 00
    00A0: 00 00 00 00 3A 4F 02 00 00 00 00 00 34 6E 02 00
    00B0: 00 00 00 00 2E 8D 02 00 00 00 00 00 28 AC 02 00
    00C0: 00 00 00 00 22 CB 02 00 00 00 00 00 1C EA 02 00
    00D0: 00 00 00 00 16 09 03 00 00 00 00 00 10 28 03 00
    00E0: 00 00 00 00 0A 47 03 00 00 00 00 00 04 66 03 00
    00F0: 00 00 00 00 FE 84 03 00 00 00 00 00 F8 A3 03 00
    0100: 00 00 00 00 F2 C2 03 00 00 00 00 00 EC E1 03 00
    0110: 00 00 00 00 E6 00 04 00 00 00 00 00 E0 1F 04 00
    0120: 00 00 00 00 DA 3E 04 00 00 00 00 00 D4 5D 04 00
    0130: 00 00 00 00 CE 7C 04 00 00 00 00 00 C8 9B 04 00
    0140: 00 00 00 00 C2 BA 04 00 00 00 00 00 BC D9 04 00
    0150: 00 00 00 00 B6 F8 04 00 00 00 00 00 .. .. .. ..

Offset | Description
$000C-000F | Offset to stored track 1.0 ($000002AC, in LO/HI format, see below for more)
$0010-0013 | Offset to stored track 1.5 ($00000000)
$0014-0017 | Offset to stored track 2.0 ($000021A6)
...
$0154-0157 | Offset to stored track 42.0 ($0004F8B6)
$0158-015B | Offset to stored track 42.5 ($00000000)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
          -----------------------------------------------
    0150: .. .. .. .. .. .. .. .. .. .. .. .. 03 00 00 00
    0160: 00 00 00 00 03 00 00 00 00 00 00 00 03 00 00 00
    0170: 00 00 00 00 03 00 00 00 00 00 00 00 03 00 00 00
    0180: 00 00 00 00 03 00 00 00 00 00 00 00 03 00 00 00
    0190: 00 00 00 00 03 00 00 00 00 00 00 00 03 00 00 00
    01A0: 00 00 00 00 03 00 00 00 00 00 00 00 03 00 00 00
    01B0: 00 00 00 00 03 00 00 00 00 00 00 00 03 00 00 00
    01C0: 00 00 00 00 03 00 00 00 00 00 00 00 03 00 00 00
    01D0: 00 00 00 00 03 00 00 00 00 00 00 00 03 00 00 00
    01E0: 00 00 00 00 02 00 00 00 00 00 00 00 02 00 00 00
    01F0: 00 00 00 00 02 00 00 00 00 00 00 00 02 00 00 00
    0200: 00 00 00 00 02 00 00 00 00 00 00 00 02 00 00 00
    0210: 00 00 00 00 02 00 00 00 00 00 00 00 01 00 00 00
    0220: 00 00 00 00 01 00 00 00 00 00 00 00 01 00 00 00
    0230: 00 00 00 00 01 00 00 00 00 00 00 00 01 00 00 00
    0240: 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00
    0250: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0260: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0270: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0290: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    02A0: 00 00 00 00 00 00 00 00 00 00 00 00 .. .. .. ..

Offset | Description
$015C-015F | Speed zone entry for track 1 ($03, in LO/HI format, see below for more)
$0160-0163 | Speed zone entry for track 1.5 ($03)
...
$02A4-02A7 | Speed zone entry for track 42 ($00)
$02A8-02AB | Speed zone entry for track 42.5 ($00)

Starting here at $02AC is the first track entry (from above, it is the first entry for track 1.0)

The track offsets (from above) require some explanation. When one is set to all 0's, no track data exists for this entry. If there is a value, it is an absolute reference into the file (starting from the beginning of the file). From the track 1.0 entry we see it is set for $000002AC. Going to that file offset, here is what we see...

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
          -----------------------------------------------
    02A0: .. .. .. .. .. .. .. .. .. .. .. .. 0C 1E FF FF
    02B0: FF FF FF 52 54 B5 29 4B 7A 5E 95 55 55 55 55 55
    02C0: 55 55 55 55 55 55 FF FF FF FF FF 55 D4 A5 29 4A
    02D0: 52 94 A5 29 4A 52 94 A5 29 4A 52 94 A5 29 4A 52

Offset | Description
$02AC-02AD | Actual size of stored track (7692 or $1E0C, in LO/HI format)
$02AE-02AE+$1E0C | Track data

Following the track data is filler bytes. In this case, there are 368 bytes of unused space. This space can contain anything, but for the sake of those wishing to compress these images for storage, they should all be set to the same value. In the sample I used, these are all set to $FF.

Below is a dump of the end of the track 1.0 data area. Note the actual track data ends at address $20B9, with the rest of the block being unused, and set to $FF.

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
          -----------------------------------------------
    1FE0: 52 94 A5 29 4A 52 94 A5 29 4A 52 94 A5 29 4A 52
    1FF0: 94 A5 29 4A 52 94 A5 29 4A 52 94 A5 29 4A 52 94
    2000: A5 29 4A 52 94 A5 29 4A 52 94 A5 29 4A 52 94 A5
    2010: 29 4A 52 94 A5 29 4A 52 94 A5 29 4A 52 94 A5 29
    2020: 4A 52 94 A5 29 4A 52 94 A5 29 4A 52 94 A5 29 4A
    2030: 55 55 55 55 55 55 FF FF FF FF FF FF FF FF FF FF
    2040: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2050: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2060: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2070: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2080: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2090: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    20A0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    20B0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    20C0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    20D0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    20E0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    20F0: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2100: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2110: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2120: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2130: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2140: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2150: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2160: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2170: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2180: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    2190: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
    21A0: FF FF FF FF FF FF .. .. .. .. .. .. .. .. .. ..

The speed offset entries can be a little more complex. The 1541 has four speed zones defined, which means the drive can write data at four distinct speeds. On a normal 1541 disk, these zones are as follows:

Track Range | Speed Zone
1-17 | 3 (highest writing speed)
18-24 | 2
25-30 | 1
31 and up | 0 (lowest writing speed)

Note that you can, through custom programming of the 1541, change the speed zone of any track to something different (change the 3 to a 0) and write data differently. From the dump of the speed offset entries above, we see that all the entries are in the range of 0-3. If any entry is less than 4, this is not considered a speed offset but defines the whole track to be recorded at that one speed.

In the example I had, there were no offsets defined, so no speed zone dump can be shown. However, I can define what should be there. You will have a block of data, 1982 bytes long. Each byte is encoded to represent the speed of 4 bytes in the track offset area, and is broken down as follows:

    Speed entry $FF:  in binary %11111111
                                 |'|'|'|'
                                 | | | |
                                 | | | +- 4'th byte speed (binary 11, 3 dec)
                                 | | +--- 3'rd byte speed (binary 11, 3 dec)
                                 | +----- 2'nd byte speed (binary 11, 3 dec)
                                 +------- 1'st byte speed (binary 11, 3 dec)

It was very smart thinking to allow for two speed zone settings, one in the offset block and another defining the speed on a per-byte basis. If you are working with a normal disk, where each track is one constant speed, then you don't need the extra blocks of information hanging around the image, wasting space.

What may not be obvious is the flexibility of this format to add tracks and speed offset zones at will. If a program decides to write a track out with varying speeds, and no speed offset exist, a new block will be created by appending it to the end of the image, and the offset pointer for that track set to point to the new block. If a track has no offset yet, meaning it doesn't exist (like a half-track), and one needs to be added, the same procedure applies. The location of the actual track or speed zone data is not important, meaning they do not have to be in any particular order since they are all referenced by the offsets at the beginning of the image.

## 16.3 The P64 NRZI flux pulse disk image format

This section is taken from "P64 file format specification" by Benjamin 'BeRo' Rosseaux.

All values are in little endian order !

### 16.3.1 P64 Header Layout

            0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
          +---------------------------------------------------------------+
    0000: |'P'|'6'|'4'|'-'|'1'|'5'|'4'|'1'|    Version    |     Flags     |
          +---------------+---------------+-------------------------------+
    0010: |     Size      | CRC32Checksum |
          +-------------------------------+

Version: File format version, current is 0x00000000 Size Size of the following whole chunk content stream Flags: Bit 0 = Write protect Bit 1-31 = Reserved, all set to 0 when creating a file, preserve existing value when updating CRC32CheckSum: CRC32 checksum of the following whole chunk content stream

### 16.3.2 P64 Chunk Header Layout

            0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
          +-----------------------------------------------+
    0000: |Chunk Signature|      Size     | CRC32Checksum |
          +-----------------------------------------------+

Chunk signature: Signature of chunk Size: Size of the chunk data CRC32CheckSum: CRC32 checksum of the chunk data

### 16.3.3 P64 Chunk 'HTPx' Layout

| x = half track index byte | +---------------------------+ Track 18 = Half track 36 = Half track index byte decimal value 36 Half track NRZI transition flux pulse data chunk block

            0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
          +---------------------------------------------------------------+
    0000: |  Count pulses |     Size      | ..... Range-encoded data .... |
          +---------------------------------------------------------------+

Count pulses: Count of the NRZI transition flux pulses in half track Size: Size of the range-encoded data

### 16.3.4 'HTPx' Range encoded data format

Hint: For a working C implememtation see p64.c and p64.h

The range coder is a FPAQ0-style range coder combined with 12-bit 0-order models, one model per byte with one bit per byte processing.

     +--------------------------------------------------------------------------+
     |   Sub stream     | Count of models |  Size per model  | Total value bits |
     +------------------+-----------------+------------------+------------------+
     |     Position     |        4        |      65536       |        32        |
     +------------------+-----------------+------------------+------------------+
     |     Strength     |        4        |      65536       |        32        |
     +------------------+-----------------+------------------+------------------+
     |   Position flag  |        1        |        2         |        1         |
     +------------------+-----------------+------------------+------------------+
     |   Strenth flag   |        1        |        2         |        1         |
     +------------------+-----------------+------------------+------------------+
     +===Total models===|        10       |==================|==================|
     +--------------------------------------------------------------------------+

All initial model state values are initialized with zero. All initial model probability values are initialized with 2048.

These model probability values will be updating in a adaptive way on the fly and not precalculated before the encoding and even not loaded before the decoding, see pseudo code below.

16000000 Hz / 5 rotations per second at 300 RPM = maximal 3200000 flux pulses So NRZI transition flux pulse positions are in the 0 .. 3199999 value range, which is also a exact single rotation, where each time unit is a cycle at 16 MHz with 300 RPM as a mapping for the ideal case. The NRZI transition flux pulse stength are in the 0x00000000 .. 0xffffffff value range, where 0xffffffff indices a strong flux pulse, that always triggers, and 0x00000001 indices a weak flux pulse, that almost never triggers, and 0x00000000 indices a flux pulse, that absolutly never triggers. For 32-bit values, the model sub streams are subdivided byte wide in a little-endian manner, and each byte is processed bitwise with model probability shifting of 4 bits, just as:

Pascal-Style pseudo code:

    procedure WriteDWord(Model, Value : longword);
    var ByteValue, ByteIndex, Context, Bit : longword;
    begin
      for ByteIndex := 0 to 3 do begin
        ByteValue := (Value shr (ByteIndex shl 3)) and $ff;
        Context := 1;
        for Bit := 7 downto 0 do begin
          Context := (Context shl 1) or RangeCoderEncodeBit(
                        RangeCoderProbabilities[
                         RangeCoderProbabilityOffsets[Model + ByteIndex] +
                         (((RangeCoderProbabilityStates[Model + ByteIndex]
                         shl 8) or Context) and $ffff)], 4, (ByteValue shr
                         Bit) and 1);
        end;
        RangeCoderProbabilityStates[Model+ByteIndex] := ByteValue;
      end;
    end;

And for 1-bit flag values it is much simpler, but also with model probability shifting of 4 bits, just as:

Pascal-Style pseudo code:

    procedure WriteBit(Model, Value : longword);
    begin
       RangeCoderProbabilityStates[Model] :=
         RangeCoderEncodeBit(RangeCoderProbabilities[
           RangeCoderProbabilityOffsets[Model] +
             RangeCoderProbabilityStates[Model]], 4, Value and 1);
    end;

The position and strength values are delta-encoded. If a value is equal to the last previous value, then the value will not encoded, instead, a flag for this will encoded. First the position value will encoded, then the stength value. If the last position delta is 0, then it is a track stream end marker.

Pascal-Style pseudo code:

    LastPosition := 0;
    PreviousDeltaPosition := 0

    LastStrength := 0;

    for PulseIndex := 0 to PulseCount - 1 do begin

      DeltaPosition := Pulses[PulseIndex].Position - LastPosition;
      if PreviousDeltaPosition <> DeltaPosition then begin
        PreviousDeltaPosition := DeltaPosition;
        WriteBit(ModelPositionFlag, 1)
        WriteDWord(ModelPosition, DeltaPosition);
      end else begin
        WriteBit(ModelPositionFlag, 0);
      end;
      LastPosition := Pulses[PulseIndex].Position;

      if LastStrength <> Pulses[PulseIndex].Strength then begin
        WriteBit(ModelStrengthFlag, 1)
        WriteDWord(ModelStrength, Pulses[PulseIndex].Strength - LastStrength);
      end else begin
        WriteBit(ModelStrengthFlag, 0);
      end;
      LastStrength := Pulses^[PulseIndex].Strength;

    end;

    // End code
    WriteBit(ModelPositionFlag, 1);
    WriteDWord(ModelPosition, 0);

The decoding is simply just in the another direction way. Pseudo code for a FPAQ0-style carryless range coder:

Pascal-Style pseudo code:

    procedure RangeCoderInit; // At encoding and decoding start
    begin
      RangeCode := 0;
      RangeLow := 0;
      RangeHigh := $ffffffff;
    end;

    procedure RangeCoderStart; // At decoding start
    var Counter : longword;
    begin
      for Counter := 1 to 4 do begin
       RangeCode := (RangeCode shl 8) or ReadByteFromInput;
      end;
    end;

    procedure RangeCoderFlush; // At encoding end
    var Counter : longword;
    begin
      for Counter := 1 to 4 do begin
        WriteByteToOutput(RangeHigh shr 24);
        RangeHigh := RangeHigh shl 8;
      end;
    end;

    procedure RangeCoderEncodeNormalize;
    begin
      while ((RangeLow xor RangeHigh) and $ff000000) = 0 do begin
       WriteByteToOutput(RangeHigh shr 24);
       RangeLow := RangeLow shl 8;
       RangeHigh := (RangeHigh shl 8) or $ff;
      end;
    end;

    function RangeCoderEncodeBit(var Probability : longword; Shift,
                                 BitValue : longword) : longword;
    begin
      RangeMiddle := RangeLow + (((RangeHigh - RangeLow) shr 12) *
                                  Probability);
      if BitValue <> 0 then begin
        inc(Probability, ($fff - Probability) shr Shift);
        RangeHigh := RangeMiddle;
      end else begin
        dec(Probability, Probability shr Shift);
        RangeLow := RangeMiddle + 1;
      end;
      RangeCoderEncodeNormalize;
      result := BitValue;
    end;

    procedure RangeCoderDecodeNormalize;
    begin
      while ((RangeLow xor RangeHigh) and $ff000000) = 0 do begin
        RangeLow := RangeLow shl 8;
        RangeHigh := (RangeHigh shl 8) or $ff;
        RangeCode := (RangeCode shl 8) or ReadByteFromInput;
      end;
    end;

    function RangeCoderDecodeBit(var Probability : longword;
                                 Shift : longword) : longword;
    begin
      RangeMiddle := RangeLow + (((RangeHigh - RangeLow) shr 12) *
                                 Probability);
      if RangeCode <= RangeMiddle then begin
        inc(Probability, ($fff - Probability) shr Shift);
        RangeHigh := RangeMiddle;
        result := 1;
      end else begin
        dec(Probability, Probability shr Shift);
        RangeLow := RangeMiddle + 1;
        result := 0;
      end;
      RangeCoderDecodeNormalize;
    end;

The probability may be never zero! But that can't happen here with this adaptive model in this P64 file format, since the adaptive model uses a shift factor of 4 bits and initial probabilities value of 2048, so the probability has a value range from 15 up to 4080 here. If you do want to use the above range coder routines for other stuff with other probability models, then you must to ensure that the probability output value is never zero, for example with "probability |= (probability < 1); " in C.

### 16.3.5 P64 Chunk 'DONE' Layout

This is the last empty chunk for to signalize that the correct file end is reached.

## 16.4 The D64 disk image format

(This section was contributed by Peter Schepers and slightly edited by Marco van den Heuvel. Added 42 track info by groepaz)

First and foremost we have D64, which is basically a sector-for-sector copy of a 1540/1541 disk. There are several versions of these which I will cover shortly. The standard D64 is a 174848 byte file comprised of 256 byte sectors arranged in 35 tracks with a varying number of sectors per track for a total of 683 sectors. Track counting starts at 1, not 0, and goes up to 35. Sector counting starts at 0, not 1, for the first sector, therefore a track with 21 sectors will go from 0 to 20.

The original media (a 5.25" disk) has the tracks laid out in circles, with track 1 on the very outside of the disk (closest to the sides) to track 35 being on the inside of the disk (closest to the inner hub ring). Commodore, in their infinite wisdom, varied the number of sectors per track and data densities across the disk to optimize available storage, resulting in the chart below. It shows the sectors/track for a standard D64. Since the outside diameter of a circle is the largest (versus closer to the center), the outside tracks have the largest amount of storage.

Track | Sectors/track | # Sectors
1-17 | 21 | 357
18-24 | 19 | 133
25-30 | 18 | 108
31-35 | 17 | 85
36-40(*) | 17 | 85
41-42(*) | 17 | 34

Track | #Sect | #SectorsIn | D64 Offset
1 | 21 | 0 | $00000
2 | 21 | 21 | $01500
3 | 21 | 42 | $02A00
4 | 21 | 63 | $03F00
5 | 21 | 84 | $05400
6 | 21 | 105 | $06900
7 | 21 | 126 | $07E00
8 | 21 | 147 | $09300
9 | 21 | 168 | $0A800
10 | 21 | 189 | $0BD00
11 | 21 | 210 | $0D200
12 | 21 | 231 | $0E700
13 | 21 | 252 | $0FC00
14 | 21 | 273 | $11100
15 | 21 | 294 | $12600
16 | 21 | 315 | $13B00
17 | 21 | 336 | $15000
18 | 19 | 357 | $16500
19 | 19 | 376 | $17800
20 | 19 | 395 | $18B00
21 | 19 | 414 | $19E00
22 | 19 | 433 | $1B100
23 | 19 | 452 | $1C400
24 | 19 | 471 | $1D700
25 | 18 | 490 | $1EA00
26 | 18 | 508 | $1FC00
27 | 18 | 526 | $20E00
28 | 18 | 544 | $22000
29 | 18 | 562 | $23200
30 | 18 | 580 | $24400
31 | 17 | 598 | $25600
32 | 17 | 615 | $26700
33 | 17 | 632 | $27800
34 | 17 | 649 | $28900
35 | 17 | 666 | $29A00
36(*) | 17 | 683 | $2AB00
37(*) | 17 | 700 | $2BC00
38(*) | 17 | 717 | $2CD00
39(*) | 17 | 734 | $2DE00
40(*) | 17 | 751 | $2EF00
41(*) | 17 | 768 | $30000
42(*) | 17 | 785 | $31100

(*) Tracks 36-40 apply to 40- and 42-track images only. (*) Tracks 41-42 apply to 42-track images only.

The directory track should be contained totally on track 18. Sectors 1-18 contain the entries and sector 0 contains the BAM (Block Availability Map) and disk name/ID. Since the directory is only 18 sectors large (19 less one for the BAM), and each sector can contain only 8 entries (32 bytes per entry), the maximum number of directory entries is 18 * 8 = 144. The first directory sector is always 18/1, even though the t/s pointer at 18/0 (first two bytes) might point somewhere else. It then follows the same chain structure as a normal file, using a sector interleave of 3. This makes the chain links go 18/1, 18/4, 18/7 etc.

Note that you can extend the directory off of track 18, but only when reading the disk or image. Attempting to write to a directory sector not on track 18 will cause directory corruption. Each directory sector has the following layout (18/1 partial dump):

     00: 12 04 81 11 00 4E 41 4D 45 53 20 26 20 50 4F 53 <- notice the T/S link
     10: 49 54 A0 A0 A0 00 00 00 00 00 00 00 00 00 15 00 <- to 18/4 ($12/$04)
     20: 00 00 84 11 02 41 44 44 49 54 49 4F 4E 41 4C 20 <- and how its not here
     30: 49 4E 46 4F A0 11 0C FE 00 00 00 00 00 00 61 01 <- ($00/$00)

The first two bytes of the sector ($12/$04) indicate the location of the next track/sector of the directory (18/4). If the track is set to $00, then it is the last sector of the directory. It is possible, however unlikely, that the directory may *not* be competely on track 18 (some disks do exist like this). Just follow the chain anyhow.

When the directory is done, the track value will be $00. The sector link should contain a value of $FF, meaning the whole sector is allocated, but the actual value doesn't matter. The drive will return all the available entries anyways.

This is a breakdown of a standard directory sector:

Bytes | Description
$00-$1F | First directory entry
$20-$3F | Second dir entry
$40-$5F | Third dir entry
$60-$7F | Fourth dir entry
$80-$9F | Fifth dir entry
$A0-$BF | Sixth dir entry
$C0-$DF | Seventh dir entry
$E0-$FF | Eighth dir entry

This is a breakdown of a standard directory entry:

Bytes | Description
$00-$01 | Track/Sector location of next directory sector ($00 $00 if not the first entry in the sector)
$02 | File type
$03-$04 | Track/sector location of first sector of file
$05-$14 | 16 character filename (in PETASCII, padded with $A0)
$15-$16 | Track/Sector location of first side-sector block (REL file only)
$17 | REL file record length (REL file only, max. value 254)
$18-$1D | Unused (except with GEOS disks)
$1E-$1F | File size in sectors, low/high byte order ($1E+$1F*256). The approx. filesize in bytes is <= #sectors * 254

The file type field is used as follows:

Bits | Description
0-3 | The actual file type
4 | Unused
5 | Used only during SAVE-@ replacement
6 | Locked flag (Set produces ">" locked files)
7 | Closed flag (Not set produces "*", or "splat" files)

The actual file type can be one of the following:

Binary | Decimal | File type
0000 | 0 | DEL
0001 | 1 | SEQ
0010 | 2 | PRG
0011 | 3 | USR
0100 | 4 | REL

Values 5-15 are illegal, but if used will produce very strange results. The 1541 is inconsistent in how it treats these bits. Some routines use all 4 bits, others ignore bit 3, resulting in values from 0-7.

Files, on a standard 1541, are stored using an interleave of 10. Assuming a starting track/sector of 17/0, the chain would run 17/0, 17/10, 17/20, 17/8, 17/18, etc.

### 16.4.1 Non-Standard & Long Directories

Most Commdore floppy disk drives use a single dedicated directory track where all filenames are stored. This limits the number of files stored on a disk based on the number of sectors on the directory track. There are some disk images that contain more files than would normally be allowed. This requires extending the directory off the default directory track by changing the last directory sector pointer to a new track, allocating the new sectors in the BAM, and manually placing (or moving existing) file entries there. The directory of an extended disk can be read and the files that reside there can be loaded without problems on a real drive. However, this is still a very dangerous practice as writing to the extended portion of the directory will cause directory corruption in the non-extended part. Many of the floppy drives core ROM routines ignore the track value that the directory is on and assume the default directory track for operations.

To explain: assume that the directory has been extended from track 18 to track 19/6 and that the directory is full except for a few slots on 19/6. When saving a new file, the drive DOS will find an empty file slot at 19/6 offset $40 and correctly write the filename and a few other things into this slot. When the file is done being saved the final file information will be written to 18/6 offset $40 instead of 19/6 causing some directory corruption to the entry at 18/6. Also, the BAM entries for the sectors occupied by the new file will not be saved and the new file will be left as a SPLAT (*) file.

Attempts to validate the disk will result in those files residing off the directory track to not be allocated in the BAM, and could also send the drive into an endless loop. The default directory track is assumed for all sector reads when validating so if the directory goes to 19/6, then the validate code will read 18/6 instead. If 18/6 is part of the normal directory chain then the validate routine will loop endlessly.

### 16.4.2 BAM layout

The layout of the BAM area (sector 18/0) is a bit more complicated...

         00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
         -----------------------------------------------
     00: 12 01 41 00 12 FF F9 17 15 FF FF 1F 15 FF FF 1F
     10: 15 FF FF 1F 12 FF F9 17 00 00 00 00 00 00 00 00
     20: 00 00 00 00 0E FF 74 03 15 FF FF 1F 15 FF FF 1F
     30: 0E 3F FC 11 07 E1 80 01 15 FF FF 1F 15 FF FF 1F
     40: 15 FF FF 1F 15 FF FF 1F 0D C0 FF 07 13 FF FF 07
     50: 13 FF FF 07 11 FF CF 07 13 FF FF 07 12 7F FF 07
     60: 13 FF FF 07 0A 75 55 01 00 00 00 00 00 00 00 00
     70: 00 00 00 00 00 00 00 00 01 08 00 00 03 02 48 00
     80: 11 FF FF 01 11 FF FF 01 11 FF FF 01 11 FF FF 01
     90: 53 48 41 52 45 57 41 52 45 20 31 20 20 A0 A0 A0
     A0: A0 A0 56 54 A0 32 41 A0 A0 A0 A0 00 00 00 00 00
     B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Bytes | Description
$00-$01 | Track/Sector location of the first directory sector (should be set to 18/1 but it doesn't matter, and don't trust what is there, always go to 18/1 for first directory entry)
$02 | Disk DOS version type (see note below) $41 ("A")
$03 | Unused
$04-$8F | BAM entries for each track, in groups of four bytes per track, starting on track 1 (see below for more details)
$90-$9F | Disk Name (padded with $A0)
$A0-$A1 | Filled with $A0
$A2-$A3 | Disk ID
$A4 | Usually $A0
$A5-$A6 | DOS type, usually "2A"
$A7-$AA | Filled with $A0
$AB | Unused ($00)
$AC-$BF | For DOLPHIN DOS track 36-40 BAM entries, otherwise unused ($00)
$C0-$D3 | For SPEED DOS track 36-40 BAM entries, otherwise unused ($00)
$D4-$FF Unused ($00)

Note: The BAM entries for SPEED, DOLPHIN and ProLogic DOS use the same layout as standard BAM entries. One of the interesting things from the BAM sector is the byte at offset $02, the DOS version byte. If it is set to anything other than $41 or $00, then we have what is called "soft write protection". Any attempt to write to the disk will return the "DOS Version" error code 73 ,"CBM DOS V 2.6 1541". The 1541 is simply telling you that it thinks the disk format version is incorrect. This message will normally come up when you first turn on the 1541 and read the error channel. If you write a $00 or a $41 into 1541 memory location $00FF (for device 0), then you can circumvent this type of write-protection, and change the DOS version back to what it should be.

The BAM entries require a bit (no pun intended) more of a breakdown. Take the first entry at bytes $04-$07 ($12 $FF $F9 $17). The first byte ($12) is the number of free sectors on that track. Since we are looking at the track 1 entry, this means it has 18 (decimal) free sectors. The next three bytes represent the bitmap of which sectors are used/free. Since it is 3 bytes (8 bits/byte) we have 24 bits of storage. Remember that at most, each track only has 21 sectors, so there are a few unused bits.

Bytes | Data | Description
$04-$07 | $12 $FF $F9 $17 | Track 1 BAM
$08-$0B | $15 $FF $FF $FF | Track 2 BAM
$0C-$0F | $15 $FF $FF $1F | Track 3 BAM
... | ... | ...
$8C-$8F | $11 $FF $FF $01 | Track 35 BAM

These entries must be viewed in binary to make any sense. We will use the first entry (track 1) at bytes 04-07:

     FF=11111111, F9=11111001, 17=00010111

In order to make any sense from the binary notation, flip the bits around.

                111111 11112222
     01234567 89012345 67890123
     --------------------------
     11111111 10011111 11101000
     ^                     ^
     sector 0           sector 20

Since we are on the first track, we have 21 sectors, and only use up to the bit 20 position. If a bit is on (1), the sector is free. Therefore, track 1 has sectors 9, 10 and 19 used, all the rest are free. Any leftover bits that refer to sectors that don't exist, like bits 21-23 in the above example, are set to allocated.

Each filetype has its own unique properties, but most follow one simple structure. The first file sector is pointed to by the directory and follows a t/s chain, until the track value reaches $00. When this happens, the value in the sector link location indicates how much of the sector is used. For example, the following chain indicates a file 6 sectors long, and ends when we encounter the $00/$34 chain. At this point the last sector occupies from bytes $02-$34.

1 | 2 | 3 | 4 | 5 | 6
---- | ---- | ---- | ---- | ---- | ----
17/0 | 17/10 | 17/20 | 17/1 | 17/11 | 0/52
(11/00) | (11/0A) | (11/14) | (11/01) | (11/0B) | (0/34)

### 16.4.3 Variations on the D64 layout

These are some variations of the D64 layout:

1. Standard 35 track layout but with 683 error bytes added on to the end of the file. Each byte of the error info corresponds to a single sector stored in the D64, indicating if the sector on the original disk contained an error. The first byte is for track 1/0, and the last byte is for track 35/16.

2. A 40 track layout, following the same layout as a 35 track disk, but with 5 extra tracks. These contain 17 sectors each, like tracks 31-35. Some of the PC utilities do allow you to create and work with these files. This can also have error bytes attached like variant #1.

3. A 42 track layout, with two extra tracks of 17 sectors each. This is extremely uncommon, since real drives often have problems with accessing these tracks, software that uses them is very rare.

4. The Commodore 128 allowed for "auto-boot" disks. With this, t/s 1/0 holds a specific byte sequence which the computer recognizes as boot code.

Below is a small chart detailing the standard file sizes of D64 images, 35, 40 or 42 tracks, with or without error bytes.

Disk type | Size
35 track, no errors | 174848
35 track, 683 error bytes | 175531
40 track, no errors | 196608
40 track, 768 error bytes | 197376
42 track, no errors | 205312
42 track, 802 error bytes | 206114

The following table (provided by Wolfgang Moser) outlines the differences between the standard 1541 DOS and the various "speeder" DOS's that exist. The 'header 7/8' category is the 'fill bytes' as the end of the sector header of a real 1541 disk.

Disk format | tracks | header 7/8 | Dos type | Diskdos vs. type
Original CBM DOS v2.6 | 35 | $0f $0f | "2A" | $41/'A'
*SpeedDOS+ | 40 | $0f $0f | "2A" | $41/'A'
Professional DOS Initial | 35 | $0f $0f | "2A" | $41/'A'
Professional DOS Version 1/Prototype | 40 | $0f $0f | "2A" | $41/'A'
ProfDOS Release | 40 | $0f $0f | "4A" | $41/'A'
Dolphin-DOS 2.0/3.0 | 35 | $0f $0f | "2A" | $41/'A'
Dolphin-DOS 2.0/3.0 | 40 | $0d $0f | "2A" | $41/'A'
PrologicDOS 1541 | 35 | $0f $0f | "2A" | $41/'A'
PrologicDOS 1541 | 40 | $0f $0f | "2P" | $50/'P'
ProSpeed 1571 2.0 | 35 | $0f $0f | "2A" | $41/'A'
ProSpeed 1571 2.0 | 40 | $0f $0f | "2P" | $50/'P'

*Note: There are also clones of SpeedDOS that exist, such as RoloDOS and DigiDOS. Both are just a change of the DOS startup string.

The location of the extra BAM information in sector 18/0, for 40 track images, will be different depending on what standard the disks have been formatted with. SPEED DOS stores them from $C0 to $D3, DOLPHIN DOS stores them from $AC to $BF and PrologicDOS stored them right after the existing BAM entries from $90-A3. PrologicDOS also moves the disk label and ID forward from the standard location of $90 to $A4. 64COPY and Star Commander let you select from several different types of extended disk formats you want to create/work with.

All three of the speeder DOS's mentioned above don't alter the standard sector interleave of 10 for files and 3 for directories. The reason is that they use a memory cache installed in the drive which reads the entire track in one pass. This alleviates the need for custom interleave values. They do seem to alter the algorithm that finds the next available free sector so that the interleave value can deviate from 10 under certain circumstances, but I don't know why they would bother.

Below is a HEX dump of a Speed DOS BAM sector. Note the location of the extra BAM info from $C0-D3.

           00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
           -----------------------------------------------
     0070: 12 FF FF 03 12 FF FF 03 12 FF FF 03 11 FF FF 01
     0080: 11 FF FF 01 11 FF FF 01 11 FF FF 01 11 FF FF 01
     0090: A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0
     00A0: A0 A0 30 30 A0 32 41 A0 A0 A0 A0 00 00 00 00 00
     00B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     00C0: 11 FF FF 01 11 FF FF 01 11 FF FF 01 11 FF FF 01
     00D0: 11 FF FF 01 00 00 00 00 00 00 00 00 00 00 00 00

Below is a HEX dump of a Dolphin DOS BAM sector. Note the location of the extra BAM info from $AC-BF.

           00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
           -----------------------------------------------
     0070: 12 FF FF 03 12 FF FF 03 12 FF FF 03 11 FF FF 01
     0080: 11 FF FF 01 11 FF FF 01 11 FF FF 01 11 FF FF 01
     0090: A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0
     00A0: A0 A0 30 30 A0 32 41 A0 A0 A0 A0 00 11 FF FF 01
     00B0: 11 FF FF 01 11 FF FF 01 11 FF FF 01 11 FF FF 01
     00C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     00D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Below is a HEX dump of a PrologicDOS BAM sector. Note that the disk name and ID are now located at $A4 instead of starting at $90.

           00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
           -----------------------------------------------
     0070: 12 FF FF 03 12 FF FF 03 12 FF FF 03 11 FF FF 01
     0080: 11 FF FF 01 11 FF FF 01 11 FF FF 01 11 FF FF 01
     0090: 11 FF FF 01 11 FF FF 01 11 FF FF 01 11 FF FF 01
     00A0: 11 FF FF 01 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0
     00B0: A0 A0 A0 A0 A0 A0 30 30 A0 32 50 A0 A0 A0 A0 00
     00C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     00D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

### 16.4.4 Error codes

Here is the meaning of the error bytes added onto the end of any extended D64. The CODE is the same as that generated by the 1541 drive controller... it reports these numbers, not the error code we usually see when an error occurs.

Some of what comes below is taken from Immers/Neufeld book "Inside Commodore DOS". Note the descriptions are not completely accurate as to what the drive DOS is actually doing to seek/read/decode/write sectors, but serve as simple examples only. The "type" field is where the error usually occurs, whether it's searching for any SYNC mark, any header ID, any valid header, or reading a sector.

Code | Error | Type | D64 | Description
$01 | 00 | N/A | * | No error.
$02 | 20 | Seek | * | Header block not found / Header descriptor byte not found
$03 | 21 | Seek | * | No SYNC sequence found
$04 | 22 | Read | * | Data descriptor byte not found
$05 | 23 | Read | * | Checksum error in data block
$06 | 24 | Write |  | Write verify on format (never occurs on 1541)
$07 | 25 | Write |  | Write verify error
$08 | 26 | Write |  | Write protect on
$09 | 27 | Seek | * | Checksum error in header block
$0A | 28 | Write |  | Write error (never occurs on 1541)
$0B | 29 | Seek | * | Disk sector ID mismatch
$0F | 74 | Read |  | Drive Not Ready (no disk in drive or no device 1)

Codes $0 and $C to $E are unused and never occur.

These first errors are "seek" errors, where the disk controller is simply reading headers and looking at descriptor bytes, checksums, format ID's and reporting what errors it sees. These errors do *not* necessarily apply to the exact sector being looked for. This fact makes duplication of these errors very unreliable.

Code : $03 Error : 21 Type : Seek Message : No SYNC sequence found.

Each sector data block and header block are preceeded by SYNC marks. If *no* sync sequence is found within 20 milliseconds (only ~1/10 of a disk rotation!) then this error is generated. This error used to mean the entire track is bad, but it does not have to be the case. Only a small area of the track needs to be without a SYNC mark and this error will be generated.

Converting this error to a D64 is very problematic because it depends on where the physical head is on the disk when a read attempt is made. If it is on valid header/sectors then it won't occur. If it happens over an area without SYNC marks, it will happen.

Code : $02 Error : 20 Type : Seek Message : Header descriptor byte not found (HEX $08, GCR $52)

Each sector is preceeded by an 8-byte GCR header block, which starts with the value $52 (GCR). If this value is not found after 90 attempts, this error is generated.

Basically, what a track has is SYNC marks, and possibly valid data blocks, but no valid header descriptors.

Code : $09 Error : 27 Type : Seek Message : Checksum error in header block

The header block contains a checksum value, calculated by XOR'ing the TRACK, SECTOR, ID1 and ID2 values. If this checksum is wrong, this error is generated.

Code : $0B Error : 29 Type : Seek Message : Disk sector ID mismatch

The ID's from the header block of the currently read sector are compared against the ones from the low-level header of 18/0. If there is a mismatch, this error is generated.

Code : $02 Error : 20 Type : Seek Message : Header block not found

This error can be reported again when searching for the correct header block. An image of the header is built and searched for, but not found after 90 read attempts. Note the difference from the first occurance. The first one only searches for a valid ID, not the whole header.

Note that error 20 occurs twice during this phase. The first time is when a header ID is being searched for, the second is when the proper header pattern for the sector being searched for is not found.

From this point on, all the errors apply to the specific sector you are looking for. If a read passed all the previous checks, then we are at the sector being searched for.

Note that the entire sector is read before these errors are detected. Therefore the data, checksum and off bytes are available.

Code : $04 Error : 22 Type : Read Message : Data descriptor byte not found (HEX $07, GCR $55)

Each sector data block is preceeded by the value $07, the "data block" descriptor. If this value is not there, this error is generated. Each encoded sector has actually 260 bytes. First is the descriptor byte, then follows the 256 bytes of data, a checksum, and two "off" bytes.

Code : $05 Error : 23 Type : Read Message : Checksum error in data block

The checksum of the data read of the disk is calculated, and compared against the one stored at the end of the sector. If there's a discrepancy, this error is generated.

Code : $0F Error : 74 Type : Read Message : Drive Not Ready (no disk in drive or no device 1)

These errors only apply when writing to a disk. I don't see the usefulness of having these as they cannot be present when only *reading* a disk.

Code : $06 Error : 24 Type : Write Message : Write verify (on format)

Code : $07 Error : 25 Type : Write Message : Write verify error

Once the GCR-encoded sector is written out, the drive waits for the sector to come around again and verifies the whole 325-byte GCR block. Any errors encountered will generate this error.

Code : $08 Error : 26 Type : Write Message : Write protect on

Self explanatory. Remove the write-protect tab, and try again.

Code : $0A Error : 28 Type : Write Message : Write error

In actual fact, this error never occurs, but it is included for completeness.

This is not an error at all, but it gets reported when the read of a sector is ok.

Code : $01 Error : 00 Type : N/A Message : No error.

Self explanatory. No errors were detected in the reading and decoding of the sector.

The advantage with using the 35 track D64 format, regardless of error bytes, is that it can be converted directly back to a 1541 disk by either using the proper cable and software on the PC, or send it down to the C64 and writing it back to a 1541. It is the best documented format since it is also native to the C64, with many books explaining the disk layout and the internals of the 1541.

## 16.5 The X64 disk image format

(This section was contributed by Peter Schepers and slightly edited by Marco van den Heuvel.)

This file type, created by Teemu Rantanen, is used on the X64 emulator (a UNIX-based emulator) which has been superceeded by VICE. Both VICE and X64 support the X64 file standard, with VICE also supporting the regular D64 and T64 files.

X64 is not a specific type of file, but rather encompasses *all* known C64 disk types (hard disk, floppies, etc). An X64 is created by prepending a 64-byte header to an existing image (1541, 1571, etc) and setting specific bytes which describe what type of image follows. This header has undergone some revision, and this description is based on the 1.02 version, which was the last known at the time of writing.

The most common X64 file you will see is the D64 variety, typically 174912 bytes long (174848 for the D64 and 64 bytes for the header, assuming no error bytes are appended). The header layout (as used in 64COPY) is as follows:

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
          -----------------------------------------------
    0000: 43 15 41 64 01 02 01 23 00 00 00 00 00 00 00 00
    0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    0040: XX XX XX <- standard C64 image starts here....

Bytes | Description
$00-$03 | This is the "Magic header" ($43 $15 $41 $64)
$04 | Header version major ($01)
$05 | Header version minor ($01, now its up to $02)
$06 | Device type represented
$07 | Maximum tracks in image (only in version 1.02 or greater) 1540/41/70: 35 1571: 35 1581: 80 (Logical single-sided disk)
$08 | Number of disk sides in image. This value must be $00 for all 1541 and 1581 formats. $00=No second side $01=Second side
$09 | Error data flag.
$0A-$1F | Unused, set to $00
$20-$3E | Disk image description (in ASCII or ISO Latin/1)
$3F | Always set to $00
$40- | Standard C64 file begins here.

The device types are:

Value | Drive type
$00 | 1540 See note below...
$01 | 1541 (Default)
$02 | 1542
$03 | 1551
$04 | 1570
$05 | 1571
$06 | 1572
$08 | 1581
$10 | 2031 or 4031
$11 | 2040 or 3040
$12 | 2041
$18 | 4040
$20 | 8050
$21 | 8060
$22 | 8061
$30 | SFD-1001
$31 | 8250
$32 | 8280

The first four bytes used for the device type at position $06 ($00 to $03) are functionally the same, and are compatible with older version of X64 files. Some old X64 files might have $00 for the device type (instead of $01), but it makes no real difference.

As most instances of X64 files will be strictly 1541 images, bytes $08-$3F are set to zero, and some versions of the X64 emulator don't use bytes $08-$3F.

## 16.6 The D71 disk image format

(This section was contributed by Peter Schepers and slightly edited by Marco van den Heuvel.)

Similar to the D64 (1541), the 1571 drive can operate in either single-sided (1541 compatible) mode or double-sided (1571) mode. In this section I will be dealing with the double-sided mode only. For the breakdown of the single-sided mode, see the D64 section.

The D71 has 70 tracks, double that of the 1541, with a DOS file size of 349696 bytes. If the error byte block (1366 bytes) is attached, this makes the file size 351062 bytes. The track range and offsets into the D71 files are as follows:

Track | Sec/trk | # Sectors
1-17 (side 0) | 21 | 357
18-24 (side 0) | 19 | 133
25-30 (side 0) | 18 | 108
31-35 (side 0) | 17 | 85
36-52 (side 1) | 21 | 357
53-59 (side 1) | 19 | 133
60-65 (side 1) | 18 | 108
66-70 (side 1) | 17 | 85

Track | #Sect | #SectorsIn | D71 Offset
1 | 21 | 0 | $00000
2 | 21 | 21 | $01500
3 | 21 | 42 | $02A00
4 | 21 | 63 | $03F00
5 | 21 | 84 | $05400
6 | 21 | 105 | $06900
7 | 21 | 126 | $07E00
8 | 21 | 147 | $09300
9 | 21 | 168 | $0A800
10 | 21 | 189 | $0BD00
11 | 21 | 210 | $0D200
12 | 21 | 231 | $0E700
13 | 21 | 252 | $0FC00
14 | 21 | 273 | $11100
15 | 21 | 294 | $12600
16 | 21 | 315 | $13B00
17 | 21 | 336 | $15000
18 | 19 | 357 | $16500
19 | 19 | 376 | $17800
20 | 19 | 395 | $18B00
21 | 19 | 414 | $19E00
22 | 19 | 433 | $1B100
23 | 19 | 452 | $1C400
24 | 19 | 471 | $1D700
25 | 18 | 490 | $1EA00
26 | 18 | 508 | $1FC00
27 | 18 | 526 | $20E00
28 | 18 | 544 | $22000
29 | 18 | 562 | $23200
30 | 18 | 580 | $24400
31 | 17 | 598 | $25600
32 | 17 | 615 | $26700
33 | 17 | 632 | $27800
34 | 17 | 649 | $28900
35 | 17 | 666 | $29A00
36 | 21 | 683 | $2AB00
37 | 21 | 704 | $2C000
38 | 21 | 725 | $2D500
39 | 21 | 746 | $2EA00
40 | 21 | 767 | $2FF00
41 | 21 | 788 | $31400
42 | 21 | 809 | $32900
43 | 21 | 830 | $33E00
44 | 21 | 851 | $35300
45 | 21 | 872 | $36800
46 | 21 | 893 | $37D00
47 | 21 | 914 | $39200
48 | 21 | 935 | $3A700
49 | 21 | 956 | $3BC00
50 | 21 | 977 | $3D100
51 | 21 | 998 | $3E600
52 | 21 | 1019 | $3FB00
53 | 19 | 1040 | $41000
54 | 19 | 1059 | $42300
55 | 19 | 1078 | $43600
56 | 19 | 1097 | $44900
57 | 19 | 1116 | $45C00
58 | 19 | 1135 | $46F00
59 | 19 | 1154 | $48200
60 | 18 | 1173 | $49500
61 | 18 | 1191 | $4A700
62 | 18 | 1209 | $4B900
63 | 18 | 1227 | $4CB00
64 | 18 | 1245 | $4DD00
65 | 18 | 1263 | $4EF00
66 | 17 | 1281 | $50100
67 | 17 | 1298 | $51200
68 | 17 | 1315 | $52300
69 | 17 | 1332 | $53400
70 | 17 | 1349 | $54500

The directory structure is the same as a D64/1541. All the same filetypes apply, the directory still only holds 144 files per disk and should only exist on track 18.

The first two bytes of the sector ($12/$04 or 18/4) indicate the location of the next track/sector of the directory. If the track value is set to $00, then it is the last sector of the directory. It is possible, however unlikely, that the directory may *not* be competely on track 18 (some disks do exist like this). Just follow the chain anyhow.

When the directory is done, the track value will be $00. The sector link should contain a value of $FF, meaning the whole sector is allocated, but the actual value doesn't matter. The drive will return all the available entries anyways. This is a breakdown of a standard directory sector and entry:

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 12 04 82 11 00 4A 45 54 20 53 45 54 20 57 49 4C
    10: 4C 59 A0 A0 A0 00 00 00 00 00 00 00 00 00 2B 00
    20: 00 00 82 0F 01 4A 53 57 20 31 A0 A0 A0 A0 A0 A0
    30: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 BF 00
    40: 00 00 82 06 03 53 4F 4E 20 4F 46 20 42 4C 41 47
    50: 47 45 52 A0 A0 00 00 00 00 00 00 00 00 00 AE 00
    60: 00 00 82 15 0D 50 4F 54 54 59 20 50 49 47 45 4F
    70: 4E A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 A2 00
    80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Bytes | Description
$00-$1F | First directory entry
$20-$3F | Second dir entry
$40-$5F | Third dir entry
$60-$7F | Fourth dir entry
$80-$9F | Fifth dir entry
$A0-$BF | Sixth dir entry
$C0-$DF | Seventh dir entry
$E0-$FF | Eighth dir entry

This is a breakdown of a standard directory entry:

Bytes | Description
$00-$01 | Track/Sector location of next directory sector ($00/$FF if its the last sector)
$02 | File type
$03-$04 | Track/sector location of first sector of file
$05-$14 | 16 character filename (in PETASCII, padded with $A0)
$15-$16 | Track/Sector location of first side-sector block (REL file only)
$17 | REL file record length (REL file only, max. value 254)
$18-$1D | Unused (except with GEOS disks)
$1E-$1F | File size in sectors, low/high byte order ($1E+$1F*256). The approx. filesize in bytes is <= #sectors * 254

The file type field is used as follows:

Bits | Description
0-3 | The actual file type
4 | Unused
5 | Used only during SAVE-@ replacement
6 | Locked flag (Set produces ">" locked files)
7 | Closed flag (Not set produces "*", or "splat" files)

The actual file type can be one of the following:

Binary | Decimal | File type
0000 | 0 | DEL
0001 | 1 | SEQ
0010 | 2 | PRG
0011 | 3 | USR
0100 | 4 | REL

Values 5-15 are illegal, but if used will produce very strange results. The 1571 is inconsistent in how it treats these bits. Some routines use all 4 bits, others ignore bit 3, resulting in values from 0-7.

When the 1571 is in is native ("1571") mode, files are stored with a sector interleave of 6, rather than 10 which the 1541 (and the 1571 in "1541" mode) uses. The directory still uses an interleave of 3.

### 16.6.1 Non-Standard & Long Directories

Most Commodore floppy disk drives use a single dedicated directory track where all filenames are stored. This limits the number of files stored on a disk based on the number of sectors on the directory track. There are some disk images that contain more files than would normally be allowed. This requires extending the directory off the default directory track by changing the last directory sector pointer to a new track, allocating the new sectors in the BAM, and manually placing (or moving existing) file entries there. The directory of an extended disk can be read and the files that reside there can be loaded without problems on a real drive. However, this is still a very dangerous practice as writing to the extended portion of the directory will cause directory corruption in the non- extended part. Many of the floppy drives core ROM routines ignore the track value that the directory is on and assume the default directory track for operations.

To explain: assume that the directory has been extended from track 18 to track 19/6 and that the directory is full except for a few slots on 19/6. When saving a new file, the drive DOS will find an empty file slot at 19/6 offset $40 and correctly write the filename and a few other things into this slot. When the file is done being saved the final file information will be written to 18/6 offset $40 instead of 19/6 causing some directory corruption to the entry at 18/6. Also, the BAM entries for the sectors occupied by the new file will not be saved and the new file will be left as a SPLAT (*) file.

Attempts to validate the disk will result in those files residing off the directory track to not be allocated in the BAM, and could also send the drive into an endless loop. The default directory track is assumed for all sector reads when validating so if the directory goes to 19/6, then the validate code will read 18/6 instead. If 18/6 is part of the normal directory chain then the validate routine will loop endlessly.

### 16.6.2 Bam layout The BAM is somewhat different as it now has to

take 35 new tracks into account. In order to do this, most of the extra BAM information is stored on track 53/0, and the remaining sectors on track 53 are marked in the BAM as allocated. This does mean that except for one allocated sector on track 53, the rest of the track is unused and wasted. (Track 53 is the equivalent to track 18, but on the flip side of the disk). Here is a dump of the first BAM sector...

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 12 01 41 80 12 FF F9 17 15 FF FF 1F 15 FF FF 1F
    10: 15 FF FF 1F 15 FF FF 1F 15 FF FF 1F 15 FF FF 1F
    20: 15 FF FF 1F 15 FF FF 1F 15 FF FF 1F 15 FF FF 1F
    30: 15 FF FF 1F 15 FF FF 1F 15 FF FF 1F 15 FF FF 1F
    40: 15 FF FF 1F 15 FF FF 1F 11 FC FF 07 13 FF FF 07
    50: 13 FF FF 07 13 FF FF 07 13 FF FF 07 13 FF FF 07
    60: 13 FF FF 07 12 FF FF 03 12 FF FF 03 12 FF FF 03
    70: 12 FF FF 03 12 FF FF 03 12 FF FF 03 11 FF FF 01
    80: 11 FF FF 01 11 FF FF 01 11 FF FF 01 11 FF FF 01
    90: A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0
    A0: A0 A0 30 30 A0 32 41 A0 A0 A0 A0 00 00 00 00 00
    B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 15 15 15
    E0: 15 15 15 15 15 15 15 15 15 15 15 15 15 15 00 13
    F0: 13 13 13 13 13 12 12 12 12 12 12 11 11 11 11 11

Bytes | Description
$00-$01 | Track/Sector location of the first directory sector (should be set to 18/1 but it doesn't matter, and don't trust what is there, always go to 18/1 for first directory entry)
$02 | Disk DOS version type (see note below) $41 ('A') = 1541
$03 | Double-sided flag $00 - Single sided disk $80 - Double sided disk
$04-8F | BAM entries for each track, in groups of four bytes per track, starting on track 1.
$90-$9F | Disk Name (padded with $A0)
$A0-$A1 | Filled with $A0
$A2-$A3 | Disk ID
$A4 | Usually $A0
$A5-$A6 | DOS type, usually "2A"
$A7-$AA | Filled with $A0
$AB-$DC | Not used ($00's)
$DD-$FF | Free sector count for tracks 36-70 (1 byte/track).

The "free sector" entries for tracks 36-70 are likely included here in the first BAM sector due to some memory restrictions in the 1571 drive. There is only enough memory available for one BAM sector, but in order to generate the "blocks free" value at the end of a directory listing, the drive needs to know the extra track "free sector" values. It does make working with the BAM a little more difficult, though.

These are the values that would normally be with the 4-byte BAM entry, but the rest of the entry is contained on 53/0.

Note: If the DOS version byte is set to anything other than $41 or $00, then we have what is called "soft write protection". Any attempt to write to the disk will return the "DOS Version" error code 73. The 1571 is simply telling you that it thinks the disk format version is incorrect.

The BAM entries require some explanation. Take the first entry at bytes $04-$07 ($12 $FF $F9 $17). The first byte ($12) is the number of free sectors on that track. Since we are looking at the track 1 entry, this means it has 18 (decimal) free sectors.

The next three bytes represent the bitmap of which sectors are used/free. Since it is 3 bytes (8 bits/byte) we have 24 bits of storage. Remember that at most, each track only has 21 sectors, so there are a few unused bits. These entries must be viewed in binary to make any sense. We will use the first entry (track 1) at bytes 04-07:

     FF=11111111, F9=11111001, 17=00010111

In order to make any sense from the binary notation, flip the bits around.

                111111 11112222
     01234567 89012345 67890123
     --------------------------
     11111111 10011111 11101000
     ^                     ^
     sector 0           sector 20

Since we are on the first track, we have 21 sectors, and only use up to the bit 20 position. If a bit is on (1), the sector is free. Therefore, track 1 has sectors 9,10 and 19 used, all the rest are free.

In order to complete the BAM, we must check 53/0.

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: FF FF 1F FF FF 1F FF FF 1F FF FF 1F FF FF 1F FF
    10: FF 1F FF FF 1F FF FF 1F FF FF 1F FF FF 1F FF FF
    20: 1F FF FF 1F FF FF 1F FF FF 1F FF FF 1F FF FF 1F
    30: FF FF 1F 00 00 00 FF FF 07 FF FF 07 FF FF 07 FF
    40: FF 07 FF FF 07 FF FF 07 FF FF 03 FF FF 03 FF FF
    50: 03 FF FF 03 FF FF 03 FF FF 03 FF FF 01 FF FF 01
    60: FF FF 01 FF FF 01 FF FF 01 00 00 00 00 00 00 00
    70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Each track from 36-70 has 3 byte entries, starting at address $00.

    Byte: $00-$02: $FF $FF $1F - BAM map for track 36
          $03-$05: $FF $FF $1F - BAM map for track 37
          ...
          $33-$35: $00 $00 $00 - BAM map for track 53
          ...
          $66-$68: $FF $FF $01 - BAM map for track 70
          $69-$FF:             - Not used

You can break down the entries for tracks 36-70 the same way as track 1, just combine the free sector bytes from 18/0 and the BAM usage from 53 to get the full 4-byte entry.

Just like a D64, you can attach error bytes to the file, for sector error information. This block is 1366 bytes long, 1 byte for each of the 1366 sectors in the image. With the error bytes, the file size is 351062 bytes.

## 16.7 The D81 disk image format

(This section was contributed by Peter Schepers and slightly edited by Marco van den Heuvel.)

Like D64 and D71, this is a byte for byte copy of a physical 1581 disk. It consists of 80 tracks, 40 sectors each (0 to 39) for a size of 819200 bytes, or 3200 sectors. If the error byte block is attached, this makes the file size 822400 bytes.

There are three sectors on the directory track used for disk internals (header and BAM), leaving 37 sectors for filename entries, thus allowing for 296 files (37 * 8) to be stored at the root level of the disk.

The actual physical layout on the disk is quite different from what the user sees, but this is unimportant to the scope of this section. One important difference from the D64 and D71 is all the sector interleaves are now 1 for both files and directory storage (rather than 3 for directory and 10 for file on a D64/D71). This is due to the built-in buffering in the 1581. When reading a sector, the whole track will be buffered in memory, and any sectors being modified will be done in memory. Once it has to be written, the whole track will be written out in one step.

The track range and offsets into the D81 files are as follows:

Track | #Sect | #SectorsIn | D81 Offset
1 | 40 | 0 | $00000
2 | 40 | 40 | $02800
3 | 40 | 80 | $05000
4 | 40 | 120 | $07800
5 | 40 | 160 | $0A000
6 | 40 | 200 | $0C800
7 | 40 | 240 | $0F000
8 | 40 | 280 | $11800
9 | 40 | 320 | $14000
10 | 40 | 360 | $16800
11 | 40 | 400 | $19000
12 | 40 | 440 | $1B800
13 | 40 | 480 | $1E000
14 | 40 | 520 | $20800
15 | 40 | 560 | $23000
16 | 40 | 600 | $25800
17 | 40 | 640 | $28000
18 | 40 | 680 | $2A800
19 | 40 | 720 | $2D000
20 | 40 | 760 | $2F800
21 | 40 | 800 | $32000
22 | 40 | 840 | $34800
23 | 40 | 880 | $37000
24 | 40 | 920 | $39800
25 | 40 | 960 | $3C000
26 | 40 | 1000 | $3E800
27 | 40 | 1040 | $41000
28 | 40 | 1080 | $43800
29 | 40 | 1120 | $46000
30 | 40 | 1160 | $48800
31 | 40 | 1200 | $4B000
32 | 40 | 1240 | $4D800
33 | 40 | 1280 | $50000
34 | 40 | 1320 | $52800
35 | 40 | 1360 | $55000
36 | 40 | 1400 | $57800
37 | 40 | 1440 | $5A000
38 | 40 | 1480 | $5C800
39 | 40 | 1520 | $5F000
40 | 40 | 1560 | $61800
41 | 40 | 1600 | $64000
42 | 40 | 1640 | $66800
43 | 40 | 1680 | $69000
44 | 40 | 1720 | $6B800
45 | 40 | 1760 | $6E000
46 | 40 | 1800 | $70800
47 | 40 | 1840 | $73000
48 | 40 | 1880 | $75800
49 | 40 | 1920 | $78000
50 | 40 | 1960 | $7A800
51 | 40 | 2000 | $7D000
52 | 40 | 2040 | $7F800
53 | 40 | 2080 | $82000
54 | 40 | 2120 | $84800
55 | 40 | 2160 | $87000
56 | 40 | 2200 | $89800
57 | 40 | 2240 | $8C000
58 | 40 | 2280 | $8E800
59 | 40 | 2320 | $91000
60 | 40 | 2360 | $93800
61 | 40 | 2400 | $96000
62 | 40 | 2440 | $98800
63 | 40 | 2480 | $9B000
64 | 40 | 2520 | $9D800
65 | 40 | 2560 | $A0000
66 | 40 | 2600 | $A2800
67 | 40 | 2640 | $A5000
68 | 40 | 2680 | $A7800
69 | 40 | 2720 | $AA000
70 | 40 | 2760 | $AC800
71 | 40 | 2800 | $AF000
72 | 40 | 2840 | $B1800
73 | 40 | 2880 | $B4000
74 | 40 | 2920 | $B6800
75 | 40 | 2960 | $B9000
76 | 40 | 3000 | $BB800
77 | 40 | 3040 | $BE000
78 | 40 | 3080 | $C0800
79 | 40 | 3120 | $C3000
80 | 40 | 3160 | $C5800

The header sector is stored at 40/0, and contains the disk name, ID and DOS version bytes, but the BAM is no longer contained here (like the D64).

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 28 03 44 00 31 35 38 31 20 55 54 49 4C 49 54 59
    10: 20 56 30 31 A0 A0 47 42 A0 33 44 A0 A0 00 00 00
    20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Bytes | Description
$00-$01 | Track/Sector location of the first directory sector (should be set to 40/3 but it doesn't matter, and don't trust what is there, always go to 40/3 for first directory entry)
$02 | Disk DOS version type (see note below) $44 ('D')=1581
$03 | $00
$04-$13 | 16 character Disk Name (padded with $A0)
$14-$15 | $A0
$16-$17 | Disk ID
$18 | $A0
$19 | DOS Version ("3")
$1A | Disk version ("D")
$1B-$1C | $A0
$1D-$FF | Unused (usually $00)

The following might be set if the disk is a GEOS format (this info is based on the D64 layout, and might not prove to be true)

Bytes | Description
$AB-$AC | Border sector (GEOS only, else set to $00)
$AD-$BC | GEOS ID string ("geos FORMAT V1.x" GEOS only, else $00)
$BD-$FF | Unused (usually $00)

Note: If the DOS version byte is changed to anything other than a $44 (or $00), then we have what is called "soft write protection". Any attempt to write to the disk will return the "DOS Version" error code 73. The drive is simply telling you that it thinks the disk format version is incompatible.

The directory track should be contained totally on track 40. Sectors 3-39 contain the entries and sector 1 and 2 contain the BAM (Block Availability Map). Sector 0 holds the disk name and ID. The first directory sector is always 40/3, even though the t/s pointer at 40/0 (first two bytes) might point somewhere else. It goes linearly up the sector count, 3-4-5-6-etc. Each sector holds up to eight entries.

The first two bytes of the sector ($28/$04) indicate the location of the next track/sector of the directory (40/4). If the track is set to $00, then it is the last sector of the directory. It is possible, however unlikely, that the directory may *not* be competely on track 40. Just follow the chain anyhow.

When the directory is done (track=$00), the sector should contain an $FF, meaning the whole sector is allocated. Theactual value doesn't matter as all the entries will be returned anyways. Each directory sector has the following layout:

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 28 04 81 2B 00 53 43 52 45 45 4E 20 20 33 A0 A0
    10: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 02 00
    20: 00 00 81 2B 01 53 43 52 45 45 4E 20 20 34 A0 A0
    30: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 03 00
    40: 00 00 81 2B 02 53 43 52 45 45 4E 20 20 35 A0 A0
    50: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 07 00
    60: 00 00 81 2B 08 53 43 52 45 45 4E 20 20 36 A0 A0
    70: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 08 00
    80: 00 00 81 2B 14 53 43 52 45 45 4E 20 20 37 A0 A0
    90: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 07 00
    A0: 00 00 81 24 00 53 43 52 45 45 4E 20 20 38 A0 A0
    B0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 0B 00
    C0: 00 00 82 24 04 46 49 4C 45 34 32 39 33 36 39 30
    D0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 07 00
    E0: 00 00 82 24 06 46 49 4C 45 32 35 37 38 38 31 35
    F0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 05 00

Bytes | Description
$00-$1F | First directory entry
$20-$3F | Second dir entry
$40-$5F | Third dir entry
$60-$7F | Fourth dir entry
$80-$9F | Fifth dir entry
$A0-$BF | Sixth dir entry
$C0-$DF | Seventh dir entry
$E0-$FF | Eighth dir entry

This is a breakdown of a standard directory entry:

Bytes | Description
$00-$01 | Track/Sector location of next directory sector
$02 | File type
$03-$04 | Track/sector location of first sector of file or partition
$05-$14 | 16 character filename (in PETASCII, padded with $A0)
$15-$16 | Track/Sector location of first SUPER SIDE SECTOR block (REL file only)
$17 | REL file record length (REL file only)
$18-$1B | Unused (except with GEOS disks)
$1C-$1D | (Used during an SAVE or OPEN, holds the new t/s link)
$1E-$1F | File or partition size in sectors, low/high byte order ($1E+$1F*256). The approx. file size in bytes is <= #sectors * 254

The file type field is used as follows:

Bits | Description
0-3 | The actual file type
4 | Unused
5 | Used only during SAVE-@ replacement
6 | Locked flag (Set produces ">" locked files)
7 | Closed flag (Not set produces "*", or "splat" files)

The actual file type can be one of the following:

Binary | Decimal | File type
0000 | 0 | DEL
0001 | 1 | SEQ
0010 | 2 | PRG
0011 | 3 | USR
0100 | 4 | REL
0101 | 5 | CBM (partition or sub-directory)

Values 6-15 are illegal, but if used will produce very strange results.

### 16.7.1 Non-Standard & Long Directories

Most Commdore floppy disk drives use a single dedicated directory track where all filenames are stored. This limits the number of files stored on a disk based on the number of sectors on the directory track. There are some disk images that contain more files than would normally be allowed. This requires extending the directory off the default directory track by changing the last directory sector pointer to a new track, allocating the new sectors in the BAM, and manually placing (or moving existing) file entries there. The directory of an extended disk can be read and the files that reside there can be loaded without problems on a real drive. However, this is still a very dangerous practice as writing to the extended portion of the directory will cause directory corruption in the non-extended part. Many of the floppy drives core ROM routines ignore the track value that the directory is on and assume the default directory track for operations.

### 16.7.2 BAM layout

The BAM is located on 40/1 (for side 0, tracks 1-40) and 40/2 (for side 1, tracks 41-80). Each entry takes up six bytes, one for the "free sector" count and five for the allocation bitmap.

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 28 02 44 BB 47 42 C0 00 00 00 00 00 00 00 00 00
    10: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    20: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    30: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF
    40: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    50: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    60: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF
    70: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    80: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    90: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF
    A0: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    B0: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    C0: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF
    D0: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    E0: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    F0: FF FF FF FF 28 FF FF FF FF FF 24 F0 FF 2D FF FE

    Bytes:
    $00-$01: Track/sector of next bam sector (40/2)
        $02: Version # ('D')
        $03: One's complement of version# ($BB)
    $04-$05: Disk ID bytes (same as 40/0 Disk ID)
        $06: I/O byte
             bit 7 set - Verify on
             bit 7 clear - Verify off
             bit 6 set - Check header CRC
             bit 6 clear - Don't check header CRC
        $07: Auto-boot-loader flag
    $08-$0F: Reserved for future (set to $00)
    $10-$15: BAM entry for track 1 (track 41, side 1)
    $16-$1B: BAM entry for track 2 (track 42, side 1)
             ...
    $46-$4B: BAM entry for track 10 (track 50, side 1)
             ...
    $82-$87: BAM entry for track 20 (track 60, side 1)
             ...
    $BE-$C3: BAM entry for track 30 (track 70, side 1)
             ...
    $FA-$FF: BAM entry for track 40 (track 80, side 1)

The BAM entries require some explanation, so lets look at the track 40 entry at bytes $FA-FF ($24 $F0 $FF $2D $FF $FE). The first byte ($24, or 36 decimal) is the number of free sectors on that track. The next five bytes represent the bitmap of which sectors are used/free. Since it is five bytes (8 bits/byte) we have 40 bits of storage. Since this format has 40 sectors/track, the whole five bytes are used.

     F0: .. .. .. .. .. .. .. .. .. .. 24 F0 FF 2D FF FE

The last five bytes of any BAM entry must be viewed in binary to make any sense. We will once again use track 40 as our reference:

     F0=11110000, FF=11111111, 2D=00101101, FF=11111111, FE=11111110

In order to make any sense from the binary notation, flip the bits around.

                       111111 11112222 22222233 33333333
     Sector 01234567 89012345 67890123 45678901 23456789
            -------------------------- -------- --------
            00001111 11111111 10110100 11111111 01111111

Note that if a bit is on (1), the sector is free. Therefore, track 40 has sectors 0-3, 17, 20, 22, 23 and 32 used, all the rest are free.

The second BAM (for side 1) contains the entries for tracks 41-80.

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 00 FF 44 BB 47 42 C0 00 00 00 00 00 00 00 00 00
    10: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    20: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    30: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF
    40: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    50: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    60: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF
    70: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    80: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    90: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF
    A0: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    B0: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    C0: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF
    D0: 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
    E0: FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF 28 FF
    F0: FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF FF FF

It is laid out exactly as the side 0 BAM except for one difference. The track/sector reference for the next sector should be set to $00/$FF, indicating there is no next sector.

### 16.7.3 REL files The REL filetype requires some extra explaining.

It was designed to make access to data *anywhere* on the disk very fast. Take a look at this directory entry...

     00: 00 FF 84 27 00 41 44 44 49 54 49 4F 4E 41 4C 20
     10: 49 4E 46 4F A0 27 02 FE 00 00 00 00 00 00 D2 0B

The third byte ($84) indicates this entry is a REL file and that the three normally empty entries at offset $15, $16 and $17 are now used as they are explained above. It's the track/sector chain that this entry points to, called the SUPER SIDE SECTOR, which is of interest here (in this case, 39/2). The SUPER SIDE SECTOR is very different from the D64 format. If you check the D64 entry for a REL file and do the calculations, you will find that the maximum file size of the REL file is 720 data sectors. With the new SUPER SIDE SECTOR, you can now have 126 groups of these SIDE SECTORS chains, allowing for file sizes up to (theoretically) 90720 sectors, or about 22.15 Megabytes.

Here is a dump of the beginning of the SUPER SIDE SECTOR...

     00: 27 01 FE 27 01 15 09 03 0F 38 16 4A 1C 00 00 00
     10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

    Bytes:
    $00-$01: Track/sector of first side sector in group 0
        $02: Always $FE
    $03-$04: Track/sector of first side sector in group 0 (again)
             ...
    $FD-$FE: Track/sector of first side sector in group 125
        $FF: Unused (likely $00)

The side sector layout is the same as the D64/1571.

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 12 0A 00 FE 15 09 12 0A 0F 0B 0C 0C 09 0D 06 0E
    10: 15 07 15 08 15 0A 15 0B 15 0C 15 0D 15 0E 15 0F
    20: 15 10 15 11 15 12 15 13 15 14 15 15 15 16 15 17
    30: 15 18 15 19 15 1A 15 1B 15 1C 15 1D 15 1E 15 1F
    40: 15 20 15 21 15 22 15 23 15 24 15 25 15 26 15 27
    50: 14 00 14 01 14 02 14 03 14 04 14 05 14 06 14 07
    60: 14 08 14 09 14 0A 14 0B 14 0C 14 0D 14 0E 14 0F
    70: 14 10 14 11 14 12 14 13 14 14 14 15 14 16 14 17
    80: 14 18 14 19 14 1A 14 1B 14 1C 14 1D 14 1E 14 1F
    90: 14 20 14 21 14 22 14 23 14 24 14 25 14 26 14 27
    A0: 13 00 13 01 13 02 13 03 13 04 13 05 13 06 13 07
    B0: 13 08 13 09 13 0A 13 0B 13 0C 13 0D 13 0E 13 0F
    C0: 13 10 13 11 13 12 13 13 13 14 13 15 13 16 13 17
    D0: 13 18 13 19 13 1A 13 1B 13 1C 13 1D 13 1E 13 1F
    E0: 13 20 13 21 13 22 13 23 13 24 13 25 13 26 13 27
    F0: 12 00 12 01 12 02 12 03 12 04 12 05 12 06 12 07

    Bytes:
        $00: Track location of next side-sector ($00 if last sector)
        $01: Sector location of next side-sector
        $02: Side-sector block number (first sector is $00, the next is
             $01, then $02, etc)
        $03: REL file RECORD size (from directory entry)
    $04-$0F: Track/sector locations of the six other side-sectors. Note
             the first entry is this very sector we have listed here.
             The next is the next t/s listed at the beginning of the
             sector. All of this information must be correct. If one of
             these chains is $00/$00, then we have no more side sectors.
             Also, all of these (up to six) side sectors must have the
             same values in this range.
    $10-$FF: T/S chains of *each* sector of the data portion. When we
             get a $00/$00, we are at the end of the file.

### 16.7.4 1581 Partitions and Sub-directories

At the beginning of this section it was stated that the 1581 can hold 296 entries "at the root level". The 1581 also has the ability to partition areas of the disk. Under the right conditions these can become sub-directories, acting as a small diskette, complete with its own directory and BAM. When you are inside of a sub-directory, no other files except those in that directory are visible, or can be affected.

To the 1581, this file will show up as a "CBM" filetype in a directory. All this does is tell the disk that a file, starting at X/Y track/sector and Z sectors large exists. Doing a validate will not harm these files as they have a directory entry, and are fully allocated in the BAM.

There are two main uses for partitions. One is to simply allocate a section of the disk to be used for direct-access reads/writes, and lock it away from being overwritten after a VALIDATE. The second is as a sub-directory, basically a small "disk within a disk".

In order to use a partition as a sub-directory, it must adhere to the following four rules:

     1. If must start on sector 0
     2. It's size must be in multiples of 40 sectors
     3. It must be a minimum of 120 sectors long (3 tracks)
     4. If must not start on or cross track 40, which limits the
        biggest directory to 1600 sectors (tracks 1-39).

This is a dump of a sub-directory entry:

     00: 00 FF 85 29 00 50 41 52 54 49 54 49 4F 4E 20 31
     10: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 40 06

It is a partition starting on track 41/0, extends for 1600 sectors, and has been formatted as a sub-directory. Note that when a partition is created, the area being allocated is not touched in any way. If you want it set up as a sub-directory, you must issue the FORMAT command to the 1581 to create the central directory and BAM. Also note that from the directory entry you can't tell whether it is a sub-directory or not, just that it fits the sub-directory parameters.

The BAM track for the sub-directory exists on the first track of the partition, and has the same layout as the disk BAM on track 40. The biggest difference is the "disk name" is what what given when the partition was formatted rather than what the actual disk name is. Also, except for the free sectors in the partition area, all other sectors in the BAM will be allocated.

If the partition size doesn't match the above rules for a sub-directory, it will simply exist as a "protected" area of the disk, and can't be used as a sub-directory. Either way, it still shows up as a "CBM" type in a directory listing. Below is a dump of a 10-sector partition starting on track 5/1, which does not qualify as a sub-directory...

     00: 00 00 85 05 01 53 4D 41 4C 4C 50 41 52 54 20 32
     10: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 0A 00

The master BAM shows the entry for this partition on track 5...

     00: 28 02 44 BB 43 44 C0 00 00 00 00 00 00 00 00 00
     10: 23 C1 FF FF FF FF 28 FF FF FF FF FF 28 FF FF FF
     20: FF FF 28 FF FF FF FF FF 1E 01 F8 FF FF FF 28 FF
                                 ^^^^^^^^^^^^^^^^^

The breakdown of the BAM shows the allocation for this track, with sectors 1-10 allocated, as it should be.

     10000000 00011111 11111111 11111111 11111111
     ^          ^          ^         ^          ^
     0          10         20        30         39

Partitions and sub-directories share one very important trait. When created, the sub-directory entry simply has the starting track/sector and the size of the partition in sectors. Partitions are created linearly, meaning if one starts on 30/1 and is of size 15 sectors, then the sector range from 1 through 15 on track 30 will be allocated. If a partition size crosses a track boundary, the allocation will continue on the next track starting on sector 0, and going up.

The section allocated will *not* have a track/sector chain like a file would, but rather is dependant on the directory entry to keep it from being overwritten. You can store whatever you want to in the allocated area.

### 16.7.5 AUTO-BOOT LOADER

If byte $07 in the BAM is set, then when the drive is reset (and other circumstances) it will look for a USR file called "COPYRIGHT CBM 86". This file will then be loaded into the drive RAM and executed.

The format for this auto-loader file is fairly basic. It starts with a two-byte load address, a size byte, program data, and a checksum at the end.

    Bytes:
           $00-$01: Load address, low/high format
               $02: Size of program (SZ) (smaller than 256 bytes)
    $03-($03+SZ-1): Program data
            $03+SZ: Checksum byte

## 16.8 The D80 disk image format

(This section was contributed by Peter Schepers and slightly edited by Marco van den Heuvel.)

This is a sector-for-sector copy of an 8050 floppy disk. The file size for an 8050 image is 533248 bytes. It is comprised of 256-byte sectors arranged across 77 tracks, with a varying number of sectors per track for a total of 2083 sectors. Track counting starts at 1 (not 0) and sector counting starts at 0 (not 1), therefore a track with 29 sectors will go from 0 to 28.

The original media (a 5.25" disk) has the tracks laid out in circles, with track 1 on the very outside of the disk (closest to the sides) to track 77 being on the inside of the disk (closest to the inner hub ring). Commodore, in their infinite wisdom, varied the number of sectors per track and data densities across the disk to optimize available storage, resulting in the chart below. It shows the sectors/track for a D80. Since the outside diameter of a circle is the largest (versus closer to the center), the outside tracks have the largest amount of storage.

Track Range | Sectors/track | # Sectors
1-39 | 29 | 1131
40-53 | 27 | 378
54-64 | 25 | 275
65-77 | 23 | 299

Track | #Sect | #SectorsIn | D8x Offset
1 | 29 | 0 | $00000
2 | 29 | 29 | $01D00
3 | 29 | 58 | $03A00
4 | 29 | 87 | $05700
5 | 29 | 116 | $07400
6 | 29 | 145 | $09100
7 | 29 | 174 | $0AE00
8 | 29 | 203 | $0CB00
9 | 29 | 232 | $0E800
10 | 29 | 261 | $10500
11 | 29 | 290 | $12200
12 | 29 | 319 | $13F00
13 | 29 | 348 | $15C00
14 | 29 | 377 | $17900
15 | 29 | 406 | $19600
16 | 29 | 435 | $1B300
17 | 29 | 464 | $1D000
18 | 29 | 493 | $1ED00
19 | 29 | 522 | $20A00
20 | 29 | 551 | $22700
21 | 29 | 580 | $24400
22 | 29 | 609 | $26100
23 | 29 | 638 | $27E00
24 | 29 | 667 | $29B00
25 | 29 | 696 | $2B800
26 | 29 | 725 | $2D500
27 | 29 | 754 | $2F200
28 | 29 | 783 | $30F00
29 | 29 | 812 | $32C00
30 | 29 | 841 | $34900
31 | 29 | 870 | $36600
32 | 29 | 899 | $38300
33 | 29 | 928 | $3A000
34 | 29 | 957 | $3BD00
35 | 29 | 986 | $3DA00
36 | 29 | 1015 | $3F700
37 | 29 | 1044 | $41400
38 | 29 | 1073 | $43100
39 | 29 | 1102 | $44E00
40 | 27 | 1131 | $46B00
41 | 27 | 1158 | $48600
42 | 27 | 1185 | $4A100
43 | 27 | 1212 | $4BC00
44 | 27 | 1239 | $4D700
45 | 27 | 1266 | $4F200
46 | 27 | 1293 | $50D00
47 | 27 | 1320 | $52800
48 | 27 | 1347 | $54300
49 | 27 | 1374 | $55E00
50 | 27 | 1401 | $57900
51 | 27 | 1428 | $59400
52 | 27 | 1455 | $5AF00
53 | 27 | 1482 | $5CA00
54 | 25 | 1509 | $5E500
55 | 25 | 1534 | $5FE00
56 | 25 | 1559 | $61700
57 | 25 | 1584 | $63000
58 | 25 | 1609 | $64900
59 | 25 | 1634 | $66200
60 | 25 | 1659 | $67B00
61 | 25 | 1684 | $69400
62 | 25 | 1709 | $6AD00
63 | 25 | 1734 | $6C600
64 | 25 | 1759 | $6DF00
65 | 23 | 1784 | $6F800
66 | 23 | 1807 | $70F00
67 | 23 | 1830 | $72600
68 | 23 | 1853 | $73D00
69 | 23 | 1876 | $75400
70 | 23 | 1899 | $76B00
71 | 23 | 1922 | $78200
72 | 23 | 1945 | $79900
73 | 23 | 1968 | $7B000
74 | 23 | 1991 | $7C700
75 | 23 | 2014 | $7DE00
76 | 23 | 2037 | $7F500
77 | 23 | 2060 | $80C00

The BAM (Block Availability Map) is on track 38. The D80 is only 77 tracks and so the BAM is contained on 38/0 and 38/3. The BAM interleave is 3.

The directory is on track 39, with 39/0 contains the header (DOS type, disk name, disk ID's) and sectors 1-28 contain the directory entries. Both files and the directory use an interleave of 1. Since the directory is only 28 sectors large (29 less one for the header), and each sector can contain only 8 entries (32 bytes per entry), the maximum number of directory entries is 28 * 8 = 224. The first directory sector is always 39/1. It then follows a chain structure using a sector interleave of 1 making the links go 39/1, 39/2, 39/3 etc.

When reading a disk, you start with 39/0 (disk label/ID) which points to 38/0 (BAM0), 38/3 (BAM1), and finally to 39/1 (first dir entry sector). When writing a file to a blank disk, it will start at 38/1 because 38/0 is already allocated.

Below is a dump of the header sector 39/0:

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 26 00 43 00 00 00 73 61 6D 70 6C 65 20 64 38 30
    10: A0 A0 A0 A0 A0 A0 A0 A0 65 72 A0 32 43 A0 A0 A0
    20: A0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ...
    F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Bytes | Description
$00-$01 | T/S pointer to first BAM sector (38/0)
$02 | $43 'C' is for DOS format version
$03 | Reserved
$04-$05 | Unused
$06-$16 | Disk name, padded with 0xA0 ("sample d80")
$17 | 0xA0
$18-$19 | Disk ID bytes "er"
$1A | 0xA0
$1B-$1C | DOS version bytes "2C"
$1D-$20 | 0xA0
$21-$FF | Unused

Below is a dump of the first directory sector, 39/1

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 27 02 82 26 01 54 45 53 54 A0 A0 A0 A0 A0 A0 A0
    10: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00
    20: 00 00 82 26 02 54 45 53 54 32 A0 A0 A0 A0 A0 A0
    30: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00
    40: 00 00 82 26 04 54 45 53 54 33 A0 A0 A0 A0 A0 A0
    50: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 05 00
    60: 00 00 82 26 0B 54 45 53 54 34 A0 A0 A0 A0 A0 A0
    70: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 09 00
    80: 00 00 82 26 14 54 45 53 54 35 A0 A0 A0 A0 A0 A0
    90: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 0C 00
    A0: 00 00 82 28 00 54 45 53 54 36 A0 A0 A0 A0 A0 A0
    B0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00
    C0: 00 00 82 28 01 54 45 53 54 37 A0 A0 A0 A0 A0 A0
    D0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00
    E0: 00 00 82 28 02 54 45 53 54 38 A0 A0 A0 A0 A0 A0
    F0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00

The first two bytes of the directory sector ($27/$02) indicate the location of the next track/sector of the directory (39/2). If the track is set to $00, then it is the last sector of the directory.

When the directory is done, the track value will be $00. The sector link should contain a value of $FF, meaning the whole sector is allocated, but the actual value doesn't matter. The drive will return all the available entries anyways. This is a breakdown of a standard directory sector:

Bytes | Description
$00-$1F | First directory entry
$20-$3F | Second dir entry
$40-$5F | Third dir entry
$60-$7F | Fourth dir entry
$80-$9F | Fifth dir entry
$A0-$BF | Sixth dir entry
$C0-$DF | Seventh dir entry
$E0-$FF | Eighth dir entry

This is a breakdown of a standard directory entry:

Bytes | Description
$00-$01 | Track/Sector location of next directory sector ($00 $00 if not the first entry in the sector)
$02 | File type
$03-$04 | Track/sector location of first sector of file
$05-$14 | 16 character filename (in PETASCII, padded with $A0)
$15-$16 | Track/Sector location of first side-sector block (REL file only)
$17 | REL file record length (REL file only, max. value 254)
$18-$1D | Unused
$1E-$1F | File size in sectors, low/high byte order ($1E+$1F*256). The approx. filesize in bytes is <= #sectors * 254

The file type field is used as follows:

Bits | Description
0-3 | The actual file type
4 | Unused
5 | Used only during SAVE-@ replacement
6 | Locked flag (Set produces ">" locked files)
7 | Closed flag (Not set produces "*", or "splat" files)

The actual file type can be one of the following:

Binary | Decimal | File type
0000 | 0 | DEL
0001 | 1 | SEQ
0010 | 2 | PRG
0011 | 3 | USR
0100 | 4 | REL

Values 5-15 are illegal, but if used will produce very strange results.

### 16.8.1 Non-Standard & Long Directories

Most Commdore floppy disk drives use a single dedicated directory track where all filenames are stored. This limits the number of files stored on a disk based on the number of sectors on the directory track. There are some disk images that contain more files than would normally be allowed. This requires extending the directory off the default directory track by changing the last directory sector pointer to a new track, allocating the new sectors in the BAM, and manually placing (or moving existing) file entries there. The directory of an extended disk can be read and the files that reside there can be loaded without problems on a real drive. However, this is still a very dangerous practice as writing to the extended portion of the directory will cause directory corruption in the non-extended part. Many of the floppy drives core ROM routines ignore the track value that the directory is on and assume the default directory track for operations.

### 16.8.2 BAM layout

The BAM only occupies up to four sectors on track 38, so the rest of the track is empty and is available for file storage. Below is a dump of the first BAM block, 38/0. A D80 will only contain two BAM sectors, 38/0 and 38/3. Each entry takes 5 bytes, 1 for the free count on that track, and 4 for the BAM bits.

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 26 03 43 00 01 33 1D FF FF FF 1F 1D FF FF FF 1F
    10: 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D
    20: FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF
    30: FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF
    40: FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF
    50: 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F
    60: 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D
    70: FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF
    80: FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF
    90: FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF
    A0: 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F
    B0: 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1B
    C0: F6 FF FF 1F 1B FC FF FF 1F 1B FF FF FF 07 1B FF
    D0: FF FF 07 1B FF FF FF 07 1B FF FF FF 07 1B FF FF
    E0: FF 07 1B FF FF FF 07 1B FF FF FF 07 1B FF FF FF
    F0: 07 1B FF FF FF 07 1B FF FF FF 07 1B FF FF FF 07

Bytes | Description
$00-$01 | T/S pointer to second BAM sector (38/3)
$02 | DOS version byte (0x43='C')
$03 | Reserved
$04 | Lowest track covered by this BAM (0x01=1)
$05 | Highest+1 track covered by this BAM (0x33=51)
$06-$0A | BAM for track 1. The first byte shows the "blocks free" for this track, the remaining 4 show the BAM for the track.
$0B-$0F | BAM for track 2
... | ...
$FB-$FF | BAM for track 50

Being bit-based, the BAM entries need some explanation. The first track entry in the above BAM sector is at offset 06, "1D FF FF FF 1F". The first number is how many blocks are free on this track ($1D=29) and the remainder is the bit representation of the usage map for the track. These entries must be viewed in binary to make any sense. First convert the values to binary:

     FF=11111111, FF=11111111, FF=11111111, 1F=00011111

In order to make any sense from the binary notation, flip the bits around.

                111111 11112222 222222
     01234567 89012345 67890123 456789...
     -------------------------- ---------
     11111111 11111111 11111111 11111000
     ^                              ^
     sector 0                   sector 28

Since we are on the first track, we have 29 sectors, and only use up to the bit 28 position. If a bit is on (1), the sector is free. Therefore, track 1 is clean, all sectors are free. Any leftover bits that refer to sectors that don't exist, like bits 29-31 in the above example, are set to allocated.

Second BAM block 38/3.

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 27 01 43 00 33 4E 1B FF FF FF 07 1B FF FF FF 07
    10: 1B FF FF FF 07 19 FF FF FF 01 19 FF FF FF 01 19
    20: FF FF FF 01 19 FF FF FF 01 19 FF FF FF 01 19 FF
    30: FF FF 01 19 FF FF FF 01 19 FF FF FF 01 19 FF FF
    40: FF 01 19 FF FF FF 01 19 FF FF FF 01 17 FF FF 7F
    50: 00 17 FF FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00
    60: 17 FF FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00 17
    70: FF FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00 17 FF
    80: FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00 00 00 00
    90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Bytes | Description
$00-$01 | T/S pointer to second BAM sector (39/1)
$02 | DOS version byte (0x43='C')
$03 | Reserved
$04 | Lowest track covered by this BAM (0x33=51)
$05 | Highest+1 track covered by this BAM (0x43=78)
$06-$0A | BAM for track 51. The first byte shows the "blocks free" for this track, the remaining 4 show the BAM for the track.
$0B-$0F | BAM for track 52
... | ...
$88-$8C | BAM for track 77
$8D-$FF | Not used

## 16.9 The D82 disk image format

(This section was contributed by Peter Schepers and slightly edited by Marco van den Heuvel.)

This is a sector-for-sector copy of an 8250 floppy disk. The file size for an 8250 image is 1066496 bytes. It is comprised of 256-byte sectors arranged across 154 tracks, with a varying number of sectors per track for a total of 4166 sectors. Track counting starts at 1 (not 0) and sector counting starts at 0 (not 1), therefore a track with 29 sectors will go from 0 to 28.

The original media (a 5.25" disk) has the tracks laid out in circles, with track 1 on the very outside of the disk (closest to the sides) to track 77 being on the inside of the disk (closest to the inner hub ring). Commodore, in their infinite wisdom, varied the number of sectors per track and data densities across the disk to optimize available storage, resulting in the chart below. It shows the sectors/track for a D82. Since the outside diameter of a circle is the largest (versus closer to the center), the outside tracks have the largest amount of storage.

Track Range | Sectors/track | # Sectors
1-39 | 29 | 1131
40-53 | 27 | 378
55-64 | 25 | 275
65-77 | 23 | 299
78-116 | 29 | 1131
117-130 | 27 | 378
131-141 | 25 | 275
142-154 | 23 | 299

Track | #Sect | #SectorsIn | D82 Offset
1 | 29 | 0 | $000000
2 | 29 | 29 | $001D00
3 | 29 | 58 | $003A00
4 | 29 | 87 | $005700
5 | 29 | 116 | $007400
6 | 29 | 145 | $009100
7 | 29 | 174 | $00AE00
8 | 29 | 203 | $00CB00
9 | 29 | 232 | $00E800
10 | 29 | 261 | $010500
11 | 29 | 290 | $012200
12 | 29 | 319 | $013F00
13 | 29 | 348 | $015C00
14 | 29 | 377 | $017900
15 | 29 | 406 | $019600
16 | 29 | 435 | $01B300
17 | 29 | 464 | $01D000
18 | 29 | 493 | $01ED00
19 | 29 | 522 | $020A00
20 | 29 | 551 | $022700
21 | 29 | 580 | $024400
22 | 29 | 609 | $026100
23 | 29 | 638 | $027E00
24 | 29 | 667 | $029B00
25 | 29 | 696 | $02B800
26 | 29 | 725 | $02D500
27 | 29 | 754 | $02F200
28 | 29 | 783 | $030F00
29 | 29 | 812 | $032C00
30 | 29 | 841 | $034900
31 | 29 | 870 | $036600
32 | 29 | 899 | $038300
33 | 29 | 928 | $03A000
34 | 29 | 957 | $03BD00
35 | 29 | 986 | $03DA00
36 | 29 | 1015 | $03F700
37 | 29 | 1044 | $041400
38 | 29 | 1073 | $043100
39 | 29 | 1102 | $044E00
40 | 27 | 1131 | $046B00
41 | 27 | 1158 | $048600
42 | 27 | 1185 | $04A100
43 | 27 | 1212 | $04BC00
44 | 27 | 1239 | $04D700
45 | 27 | 1266 | $04F200
46 | 27 | 1293 | $050D00
47 | 27 | 1320 | $052800
48 | 27 | 1347 | $054300
49 | 27 | 1374 | $055E00
50 | 27 | 1401 | $057900
51 | 27 | 1428 | $059400
52 | 27 | 1455 | $05AF00
53 | 27 | 1482 | $05CA00
54 | 25 | 1509 | $05E500
55 | 25 | 1534 | $05FE00
56 | 25 | 1559 | $061700
57 | 25 | 1584 | $063000
58 | 25 | 1609 | $064900
59 | 25 | 1634 | $066200
60 | 25 | 1659 | $067B00
61 | 25 | 1684 | $069400
62 | 25 | 1709 | $06AD00
63 | 25 | 1734 | $06C600
64 | 25 | 1759 | $06DF00
65 | 23 | 1784 | $06F800
66 | 23 | 1807 | $070F00
67 | 23 | 1830 | $072600
68 | 23 | 1853 | $073D00
69 | 23 | 1876 | $075400
70 | 23 | 1899 | $076B00
71 | 23 | 1922 | $078200
72 | 23 | 1945 | $079900
73 | 23 | 1968 | $07B000
74 | 23 | 1991 | $07C700
75 | 23 | 2014 | $07DE00
76 | 23 | 2037 | $07F500
77 | 23 | 2060 | $080C00
78 | 29 | 2083 | $082300
79 | 29 | 2112 | $084000
80 | 29 | 2141 | $085D00
81 | 29 | 2170 | $087A00
82 | 29 | 2199 | $089700
83 | 29 | 2228 | $08B400
84 | 29 | 2257 | $08D100
85 | 29 | 2286 | $08EE00
86 | 29 | 2315 | $090600
87 | 29 | 2344 | $092800
88 | 29 | 2373 | $094500
89 | 29 | 2402 | $096200
90 | 29 | 2431 | $097F00
91 | 29 | 2460 | $099C00
92 | 29 | 2489 | $09B900
93 | 29 | 2518 | $09D600
94 | 29 | 2547 | $09F300
95 | 29 | 2576 | $0A1000
96 | 29 | 2605 | $0A2D00
97 | 29 | 2634 | $0A4A00
98 | 29 | 2663 | $0A6700
99 | 29 | 2692 | $0A8400
100 | 29 | 2721 | $0AA100
101 | 29 | 2750 | $0ABE00
102 | 29 | 2779 | $0ADB00
103 | 29 | 2808 | $0AF800
104 | 29 | 2837 | $0B1500
105 | 29 | 2866 | $0B3200
106 | 29 | 2895 | $0B4F00
107 | 29 | 2924 | $0B6C00
108 | 29 | 2953 | $0B8900
109 | 29 | 2982 | $0BA600
110 | 29 | 3011 | $0BC300
111 | 29 | 3040 | $0BE000
112 | 29 | 3069 | $0BFD00
113 | 29 | 3098 | $0C1A00
114 | 29 | 3137 | $0C3700
115 | 29 | 3156 | $0C5400
116 | 29 | 3185 | $0C7100
117 | 27 | 3214 | $0C8E00
118 | 27 | 3241 | $0CA900
119 | 27 | 3268 | $0CC400
120 | 27 | 3295 | $0CDF00
121 | 27 | 3322 | $0CFA00
122 | 27 | 3349 | $0D1500
123 | 27 | 3376 | $0D3000
124 | 27 | 3403 | $0D4B00
125 | 27 | 3430 | $0D6600
126 | 27 | 3457 | $0D8100
127 | 27 | 3484 | $0D9C00
128 | 27 | 3511 | $0DB700
129 | 27 | 3538 | $0DD200
130 | 27 | 3565 | $0DED00
131 | 25 | 3592 | $0E0800
132 | 25 | 3617 | $0E2100
133 | 25 | 3642 | $0E3A00
134 | 25 | 3667 | $0E5300
135 | 25 | 3692 | $0E6C00
136 | 25 | 3717 | $0E8500
137 | 25 | 3742 | $0E9E00
138 | 25 | 3767 | $0EB700
139 | 25 | 3792 | $0ED000
140 | 25 | 3817 | $0EE900
141 | 25 | 3842 | $0F0200
142 | 23 | 3867 | $0F1B00
143 | 23 | 3890 | $0F3200
144 | 23 | 3913 | $0F4900
145 | 23 | 3936 | $0F6000
146 | 23 | 3959 | $0F7700
147 | 23 | 3982 | $0F8E00
148 | 23 | 4005 | $0FA500
149 | 23 | 4028 | $0FBC00
150 | 23 | 4051 | $0FD300
151 | 23 | 4074 | $0FEA00
152 | 23 | 4097 | $100100
153 | 23 | 4120 | $101800
154 | 23 | 4143 | $102F00

The BAM (Block Availability Map) is on track 38. The D82 is 154 tracks and so the BAM is contained on 38/0, 38/3, 38/6 and 38/9. The BAM interleave is 3.

The directory is on track 39, with 39/0 contains the header (DOS type, disk name, disk ID's) and sectors 1-28 contain the directory entries. Both files and the directory use an interleave of 1. Since the directory is only 28 sectors large (29 less one for the header), and each sector can contain only 8 entries (32 bytes per entry), the maximum number of directory entries is 28 * 8 = 224. The first directory sector is always 39/1. It then follows a chain structure using a sector interleave of 1 making the links go 39/1, 39/2, 39/3 etc.

When reading a disk, you start with 39/0 (disk label/ID) which points to 38/0 (BAM0), 38/3 (BAM1), 38/6 (BAM2), 38/9 (BAM3, and finally to 39/1 (first dir entry sector). When writing a file to a blank disk, it will start at 38/1 because 38/0 is already allocated.

Below is a dump of the header sector 39/0:

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 26 00 43 00 00 00 73 61 6D 70 6C 65 20 64 38 30
    10: A0 A0 A0 A0 A0 A0 A0 A0 65 72 A0 32 43 A0 A0 A0
    20: A0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ...
    F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Bytes | Description
$00-$01 | T/S pointer to first BAM sector (38/0)
$02 | $43 'C' is for DOS format version
$03 | Reserved
$04-$05 | Unused
$06-$16 | Disk name, padded with 0xA0 ("sample d82")
$17 | 0xA0
$18-$19 | Disk ID bytes "er"
$1A | 0xA0
$1B-$1C | DOS version bytes "2C"
$1D-$20 | 0xA0
$21-$FF | Unused

Below is a dump of the first directory sector, 39/1

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 27 02 82 26 01 54 45 53 54 A0 A0 A0 A0 A0 A0 A0
    10: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00
    20: 00 00 82 26 02 54 45 53 54 32 A0 A0 A0 A0 A0 A0
    30: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00
    40: 00 00 82 26 04 54 45 53 54 33 A0 A0 A0 A0 A0 A0
    50: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 05 00
    60: 00 00 82 26 0B 54 45 53 54 34 A0 A0 A0 A0 A0 A0
    70: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 09 00
    80: 00 00 82 26 14 54 45 53 54 35 A0 A0 A0 A0 A0 A0
    90: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 0C 00
    A0: 00 00 82 28 00 54 45 53 54 36 A0 A0 A0 A0 A0 A0
    B0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00
    C0: 00 00 82 28 01 54 45 53 54 37 A0 A0 A0 A0 A0 A0
    D0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00
    E0: 00 00 82 28 02 54 45 53 54 38 A0 A0 A0 A0 A0 A0
    F0: A0 A0 A0 A0 A0 00 00 00 00 00 00 00 00 00 01 00

The first two bytes of the directory sector ($27/$02) indicate the location of the next track/sector of the directory (39/2). If the track is set to $00, then it is the last sector of the directory.

When the directory is done, the track value will be $00. The sector link should contain a value of $FF, meaning the whole sector is allocated, but the actual value doesn't matter. The drive will return all the available entries anyways. This is a breakdown of a standard directory sector:

Bytes | Description
$00-$1F | First directory entry
$20-$3F | Second dir entry
$40-$5F | Third dir entry
$60-$7F | Fourth dir entry
$80-$9F | Fifth dir entry
$A0-$BF | Sixth dir entry
$C0-$DF | Seventh dir entry
$E0-$FF | Eighth dir entry

This is a breakdown of a standard directory entry:

Bytes | Description
$00-$01 | Track/Sector location of next directory sector ($00 $00 if not the first entry in the sector)
$02 | File type
$03-$04 | Track/sector location of first sector of file
$05-$14 | 16 character filename (in PETASCII, padded with $A0)
$15-$16 | Track/Sector location of first side-sector block (REL file only)
$17 | REL file record length (REL file only, max. value 254)
$18-$1D | Unused
$1E-$1F | File size in sectors, low/high byte order ($1E+$1F*256). The approx. filesize in bytes is <= #sectors * 254

The file type field is used as follows:

Bits | Description
0-3 | The actual file type
4 | Unused
5 | Used only during SAVE-@ replacement
6 | Locked flag (Set produces ">" locked files)
7 | Closed flag (Not set produces "*", or "splat" files)

The actual file type can be one of the following:

Binary | Decimal | File type
0000 | 0 | DEL
0001 | 1 | SEQ
0010 | 2 | PRG
0011 | 3 | USR
0100 | 4 | REL

Values 5-15 are illegal, but if used will produce very strange results.

### 16.9.1 Non-Standard & Long Directories

Most Commdore floppy disk drives use a single dedicated directory track where all filenames are stored. This limits the number of files stored on a disk based on the number of sectors on the directory track. There are some disk images that contain more files than would normally be allowed. This requires extending the directory off the default directory track by changing the last directory sector pointer to a new track, allocating the new sectors in the BAM, and manually placing (or moving existing) file entries there. The directory of an extended disk can be read and the files that reside there can be loaded without problems on a real drive. However, this is still a very dangerous practice as writing to the extended portion of the directory will cause directory corruption in the non-extended part. Many of the floppy drives core ROM routines ignore the track value that the directory is on and assume the default directory track for operations.

### 16.9.2 BAM layout

The BAM only occupies up to four sectors on track 38, so the rest of the track is empty and is available for file storage. Below is a dump of the first BAM block, 38/0. A D82 will contain four BAM sectors, 38/0, 38/3, 38/6 and 38/9. Each entry takes 5 bytes, 1 for the free count on that track, and 4 for the BAM bits.

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 26 03 43 00 01 33 1D FF FF FF 1F 1D FF FF FF 1F
    10: 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D
    20: FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF
    30: FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF
    40: FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF
    50: 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F
    60: 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D
    70: FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF
    80: FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF
    90: FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF
    A0: 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F
    B0: 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1B
    C0: F6 FF FF 1F 1B FC FF FF 1F 1B FF FF FF 07 1B FF
    D0: FF FF 07 1B FF FF FF 07 1B FF FF FF 07 1B FF FF
    E0: FF 07 1B FF FF FF 07 1B FF FF FF 07 1B FF FF FF
    F0: 07 1B FF FF FF 07 1B FF FF FF 07 1B FF FF FF 07

Bytes | Description
$00-$01 | T/S pointer to second BAM sector (38/3)
$02 | DOS version byte (0x43='C')
$03 | Reserved
$04 | Lowest track covered by this BAM (0x01=1)
$05 | Highest+1 track covered by this BAM (0x33=51)
$06-$0A | BAM for track 1. The first byte shows the "blocks free" for this track, the remaining 4 show the BAM for the track.
$0B-$0F | BAM for track 2
... | ...
$FB-$FF | BAM for track 50

Being bit-based, the BAM entries need some explanation. The first track entry in the above BAM sector is at offset 06, "1D FF FF FF 1F". The first number is how many blocks are free on this track ($1D=29) and the remainder is the bit representation of the usage map for the track. These entries must be viewed in binary to make any sense. First convert the values to binary:

     FF=11111111, FF=11111111, FF=11111111, 1F=00011111

In order to make any sense from the binary notation, flip the bits around.

                111111 11112222 222222
     01234567 89012345 67890123 456789...
     -------------------------- ---------
     11111111 11111111 11111111 11111000
     ^                              ^
     sector 0                  sector 28

Since we are on the first track, we have 29 sectors, and only use up to the bit 28 position. If a bit is on (1), the sector is free. Therefore, track 1 is clean, all sectors are free. Any leftover bits that refer to sectors that don't exist, like bits 29-31 in the above example, are set to allocated.

Second BAM block 38/3

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 26 06 43 00 33 65 1B FF FF FF 07 1B FF FF FF 07
    10: 1B FF FF FF 07 19 FF FF FF 01 19 FF FF FF 01 19
    20: FF FF FF 01 19 FF FF FF 01 19 FF FF FF 01 19 FF
    30: FF FF 01 19 FF FF FF 01 19 FF FF FF 01 19 FF FF
    40: FF 01 19 FF FF FF 01 19 FF FF FF 01 17 FF FF 7F
    50: 00 17 FF FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00
    60: 17 FF FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00 17
    70: FF FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00 17 FF
    80: FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00 1D FF FF
    90: FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF
    A0: 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F
    B0: 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D
    C0: FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF
    D0: FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF
    E0: FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF
    F0: 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F

Bytes | Description
$00-$01 | T/S pointer to third BAM sector (38/6)
$02 | DOS version byte (0x43='C')
$03 | Reserved
$04 | Lowest track covered by this BAM (0x33=51)
$05 | Highest+1 track covered by this BAM (0x65=101)
$06-$0A | BAM for track 51. The first byte shows the "blocks free" for this track, the remaining 4 show the BAM for the track.
$0B-$0F | BAM for track 52
... | ...
$FB-$FF | BAM for track 100

Third BAM block 38/6

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 26 09 43 00 65 97 1D FF FF FF 1F 1D FF FF FF 1F
    10: 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D
    20: FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF
    30: FF FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF
    40: FF 1F 1D FF FF FF 1F 1D FF FF FF 1F 1D FF FF FF
    50: 1F 1D FF FF FF 1F 1B FF FF FF 07 1B FF FF FF 07
    60: 1B FF FF FF 07 1B FF FF FF 07 1B FF FF FF 07 1B
    70: FF FF FF 07 1B FF FF FF 07 1B FF FF FF 07 1B FF
    80: FF FF 07 1B FF FF FF 07 1B FF FF FF 07 1B FF FF
    90: FF 07 1B FF FF FF 07 1B FF FF FF 07 19 FF FF FF
    A0: 01 19 FF FF FF 01 19 FF FF FF 01 19 FF FF FF 01
    B0: 19 FF FF FF 01 19 FF FF FF 01 19 FF FF FF 01 19
    C0: FF FF FF 01 19 FF FF FF 01 19 FF FF FF 01 19 FF
    D0: FF FF 01 17 FF FF 7F 00 17 FF FF 7F 00 17 FF FF
    E0: 7F 00 17 FF FF 7F 00 17 FF FF 7F 00 17 FF FF 7F
    F0: 00 17 FF FF 7F 00 17 FF FF 7F 00 17 FF FF 7F 00

Bytes | Description
$00-$01 | T/S pointer to fourth BAM sector (38/9)
$02 | DOS version byte (0x43='C')
$03 | Reserved
$04 | Lowest track covered by this BAM (0x65=101)
$05 | Highest+1 track covered by this BAM (0x97=151)
$06-$0A | BAM for track 101. The first byte shows the "blocks free" for this track, the remaining 4 show the BAM for the track.
$0B-$0F | BAM for track 102
... | ...
$FB-$FF | BAM for track 150

Fourth BAM block 38/9

        00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
        -----------------------------------------------
    00: 27 01 43 00 97 9B 17 FF FF 7F 00 17 FF FF 7F 00
    10: 17 FF FF 7F 00 17 FF FF 7F 00 00 00 00 00 00 00
    20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Bytes | Description
$00-$01 | T/S pointer to first directory sector (39/1)
$02 | DOS version byte (0x43='C')
$03 | Reserved
$04 | Lowest track covered by this BAM (0x97=151)
$05 | Highest+1 track covered by this BAM (0x9B=155)
$06-$0A | BAM for track 151. The first byte shows the "blocks free" for this track, the remaining 4 show the BAM for the track.
$0B-$0F | BAM for track 152
... | ...
$15-$19 | BAM for track 154
$1A-$FF | Not used

## 16.10 The P00 image format

(This section was contributed by Peter Schepers and slightly edited by Marco van den Heuvel.)

These files were created for use in the PC64 emulator, written by Wolfgang Lorenz. Each one has the same layout with the filetype being stored in the DOS extension (i.e. Pxx is a PRG, Sxx is a SEQ, Uxx is a USR and Rxx is a RELative file), and the header is only 26 bytes long.

This is a dump of a Pxx file (PRG)...

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
          -----------------------------------------------
    0000: 43 36 34 46 69 6C 65 00 43 52 49 53 49 53 20 4D
    0010: 4F 55 4E 54 41 49 4E 00 00 00

Bytes | Description
$00-$06 | ASCII string "C64File"
$07 | Always $00
$08-$17 | Filename in PETASCII, padded with $00 (not $A0, like a D64)
$18 | Always $00
$19 | REL file record size ($00 if not a REL file)
$1A-?? | Program data

The 'xx' in the extension of the file is usually 00, except when we have two DOS filenames which would be the same, but the C64 filenames are different! If we have two C64 filenames which are the same, they *cannot* co-exist in the same directory. If we have two files which do convert down to be the same DOS filename, the extension is incremented until an unused one is found (x01, x02, x03, up to x99). We can have up to 99 different C64 files with the same corresponding DOS names as that's all the extension will hold (from P00 to P99).

Each PC64 file only has one entry, there are no multi-file containers allowed. This could result in a large number of these files in a directory, even for only a few programs, as each C64 file will result in a PC64 file entry. The best use for a PC64 file is a single-file program, one which does not load anything else.

## 16.11 The CRT cartridge image format

This chapter is based on CRT.txt (rev1.14) compiled by Peter Schepers, with additional contributions from Per Hakan Sundell, Markus Brenner, Marco Van Den Heuvel, Groepaz.

Cartridge files were introduced in the CCS64 emulator, written by Per Hakan Sundell, and use the ".CRT" file extension. This format was created to handle the various ROM cartridges that exist, such as Action Replay, the Power cartridge, and the Final Cartridge.

Normal game cartridges can load into several different memory ranges ($8000-9FFF, $A000-BFFF or $E000-FFFF). Newer utility and freezer cartridges were less intrusive, hiding themselves until called upon, and still others used bank-switching techniques to allow much larger ROM's than normal. Because of these "stealthing" and bank-switching methods, a special cartridge format was necessary, to let the emulator know where the cartridge should reside, the control line states to enable it and any special hardware features it uses.

### 16.11.1 Header contents

Here is a dump of a sample 8K normal cartridge, "Attack Of The Mutant Camels"...

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 00 00 01 00 00 00 00 00 00   ???@????????????
    0020: 41 54 54 41 43 4B 20 4F 46 20 54 48 45 20 4D 55   ATTACK?OF?THE?MU
    0030: 54 41 4E 54 20 43 41 4D 45 4C 53 00 00 00 00 00   TANT?CAMELS?????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0050: D3 9B BC FE C3 C2 CD 38 30 EA EA EA A9 01 85 13   .?....80....??
    0060: 4C B3 9B A9 08 85 5A 88 D0 FD C6 5A D0 F9 60 D0   L³.?Z...Z.?`.

      Bytes:$0000-000F - 16-byte cartridge signature  "C64  CARTRIDGE"  (padded
                         with space characters)
             0010-0013 - File header length  ($00000040,  in  high/low  format,
                         calculated from offset $0000). The default  (also  the
                         minimum) value is $40.  Some  cartridges  exist  which
                         show a value of $00000020 which is wrong.
             0014-0015 - Cartridge version (high/low, presently 01.00)
             0016-0017 - Cartridge hardware type ($0000, high/low)
                           0 - Normal cartridge
                           1 - Action Replay
                           2 - KCS Power Cartridge
                           3 - Final Cartridge III
                           4 - Simons' BASIC
                           5 - Ocean type 1*
                           6 - Expert Cartridge
                           7 - Fun Play, Power Play
                           8 - Super Games
                           9 - Atomic Power
                          10 - Epyx Fastload
                          11 - Westermann Learning
                          12 - Rex Utility
                          13 - Final Cartridge I
                          14 - Magic Formel
                          15 - C64 Game System, System 3
                          16 - Warp Speed
                          17 - Dinamic**
                          18 - Zaxxon, Super Zaxxon (SEGA)
                          19 - Magic Desk, Domark, HES Australia
                          20 - Super Snapshot V5
                          21 - Comal-80
                          22 - Structured BASIC
                          23 - Ross
                          24 - Dela EP64
                          25 - Dela EP7x8
                          26 - Dela EP256
                          27 - Rex EP256
                          28 - Mikro Assembler
                          29 - Final Cartridge Plus
                          30 - Action Replay 4
                          31 - Stardos
                          32 - EasyFlash
                          33 - EasyFlash Xbank
                          34 - Capture
                          35 - Action Replay 3
                          36 - Retro Replay
                          37 - MMC64
                          38 - MMC Replay
                          39 - IDE64
                          40 - Super Snapshot V4
                          41 - IEEE-488
                          42 - Game Killer
                          43 - Prophet64
                          44 - EXOS
                          45 - Freeze Frame
                          46 - Freeze Machine
                          47 - Snapshot64
                          48 - Super Explode V5.0
                          49 - Magic Voice
                          50 - Action Replay 2
                          51 - MACH 5
                          52 - Diashow-Maker
                          53 - Pagefox
                          54 - Kingsoft
                          55 - Silverrock 128K Cartridge
                          56 - Formel 64
                          57 - RGCD
                  0018 - Cartridge port EXROM line status
                          0 - active (lo)
                          1 - inactive (hi)
                  0019 - Cartridge port GAME line status
                          0 - active (lo)
                          1 - inactive (hi)
             001A-001F - Reserved for future use
             0020-003F - 32-byte cartridge  name  "CCSMON"  (uppercase,  padded
                         with null characters)
             0040-xxxx - Cartridge contents (called CHIP PACKETS, as there  can
                         be more than one  per  CRT  file).  See  below  for  a
                         breakdown of the CHIP format.

(*Note: Ocean type 1 includes Navy Seals, Robocop 2 & 3, Shadow of the Beast, Toki, Terminator 2 and more)

(**Note: Dinamic includes Narco Police and more)

### 16.11.2 CHIP Contents

The following is the contents of the CHIP packet, from position $0040 on in the CRT file. Note I have re-adjusted the starting address to be $0000, since we are now looking at a file contained in the .CRT file, and all size references are from where it starts.

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0010: D3 9B BC FE C3 C2 CD 38 30 EA EA EA A9 01 85 13   .?....80....??
    0020: 4C B3 9B A9 08 85 5A 88 D0 FD C6 5A D0 F9 60 D0   L³.?Z...Z.?`.
    0030: F2 60 A9 04 85 49 A9 00 85 48 A2 00 A5 48 9D 40   ?`.?I.?H.?¥H@
    0040: 03 A5 49 9D 60 03 A5 48 18 69 28 85 48 A5 49 69   ?¥I`?¥H?i(H¥Ii
    0050: 00 85 49 E8 E0 18 D0 E4 60 A6 03 A4 02 BD 40 03   ?I???.?`?????@?

      Bytes:$0000-0003 - Contained ROM signature "CHIP" (note there can be more
                         than one image in a .CRT file)
             0004-0007 - Total packet length ($00002010,  ROM  image  size  and
                         header combined) (high/low format)
             0008-0009 - Chip type
                          0 - ROM
                          1 - RAM, no ROM data
                          2 - Flash ROM
             000A-000B - Bank number ($0000 - normal cartridge)
             000C-000D - Starting load address (high/low format)
             000E-000F - ROM image size in bytes  (high/low  format,  typically
                         $2000 or $4000)
             0010-xxxx - ROM data

The following is a chart taken from the "Commodore Programmers Reference Guide". It details the state of various areas of memory depending on the state of the control lines.

Legend: L - ROML (low) H - ROMH (high) G - GAME E - EXROM

    Addr       LHGE   LHGE   LHGE   LHGE   LHGE   LHGE   LHGE   LHGE   LHGE
    Range
               1111   101X   1000   011X   001X   1110   0100   1100   XX01
             default                00X0                             Ultimax
    -------------------------------------------------------------------------
    E000-FFFF Kernal  RAM    RAM   Kernal  RAM   Kernal Kernal Kernal ROMH(*)
    D000-DFFF IO/CHR IO/CHR IO/RAM IO/CHR  RAM   IO/CHR IO/CHR IO/CHR   I/O
    C000-CFFF  RAM    RAM    RAM    RAM    RAM    RAM    RAM    RAM     -
    A000-BFFF BASIC   RAM    RAM    RAM    RAM   BASIC   ROMH   ROMH    -
    8000-9FFF  RAM    RAM    RAM    RAM    RAM    ROML   RAM    ROML  ROML(*)
    4000-7FFF  RAM    RAM    RAM    RAM    RAM    RAM    RAM    RAM     -
    1000-3FFF  RAM    RAM    RAM    RAM    RAM    RAM    RAM    RAM     -
    0000-0FFF  RAM    RAM    RAM    RAM    RAM    RAM    RAM    RAM    RAM

(*) Internal memory does not respond to write accesses in these areas

From the above chart, the following table can be built. It shows standard cartridges, either 8K or 16K in size, and the memory ranges they load into.

    Type     Size   Game   EXRom  Low Bank  High Bank
             in K   Line   Line    (ROML)    (ROMH)
    -------------------------------------------------
    Normal    8k     hi     lo     $8000      ----
    Normal    16k    lo     lo     $8000     $A000
    Ultimax   8k     lo     hi     $E000      ----

The ROMH and ROML lines are CPU-controlled status lines, used to bank in/out RAM, ROM or I/O, depending on what is needed at the time.

Ultimax cartridges typically are situated in the $E000-FFFF (8K) ROM address range. There are some cartridges which only use 4K of the 8K allocation. If the cartridge is 16K in size, then it will reside in both $8000-9FFF and $E000-FFFF.

### 16.11.3 Cartridge Specifics

#### 16.11.3.1 0 - Normal cartridge

Size | 8Kb
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 00 00 01 00 00 00 00 00 00   ???@????????????
    0020: 41 54 54 41 43 4B 20 4F 46 20 54 48 45 20 4D 55   ATTACK?OF?THE?MU
    0030: 54 41 4E 54 20 43 41 4D 45 4C 53 00 00 00 00 00   TANT?CAMELS?????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0050: D3 9B BC FE C3 C2 CD 38 30 EA EA EA A9 01 85 13   .?....80....??

The second sample below is a dump of "Music Machine", a 4Kb ULTIMAX mode cartridge. It is still identified as a "standard cartridge" according to the ID.

Normal cartridge

Size | 4Kb (ULTIMAX mode)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $F000-F7FF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 00 01 00 00 00 00 00 00 00   ???@????????????
    0020: 4D 55 53 49 43 20 4D 41 43 48 49 4E 45 00 00 00   MUSIC?MACHINE???
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 10 10 00 00 00 00 F0 00 10 00   CHIP????????????
    0050: 3C 66 C3 C3 66 3C FF FF 18 3C 66 7E 66 66 66 00   <f..f<???<f~fff?

The third sample is a dump of "Adventure Creator", a 16Kb standard cartridge.

Normal cartridge

Size | 16Kb
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $8000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 00 00 00 00 00 00 00 00 00   ???@????????????
    0020: 41 64 76 65 6E 74 75 72 65 20 43 72 65 61 74 6F   Adventure?Creato
    0030: 72 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   r???????????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00   CHIP???????.?@?
    0050: 09 80 81 EA C3 C2 CD 38 30 A2 00 78 D8 8E 11 D0   ?.....80.?x.?.

#### 16.11.3.2 1 - Action Replay

Size | 32Kb (4 banks of 8Kb each)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $8000-9FFF (all modules)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 01 00 00 00 00 00 00 00 00   ???@????????????
    0020: 41 63 74 69 6F 6E 20 52 65 70 6C 61 79 20 56 00   Action?Replay?V?
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0050: 09 80 0C 80 C3 C2 CD 38 30 4C 60 80 4C 63 80 4C   ?.?....80L`.Lc.L

This cart has 32Kb of ROM, and 8Kb of RAM. The bank switching is done by writing to the I/O-1 range as follows:

        bit  meaning
        ---  -------
        7    extra ROM bank selector (A15) (unused)
        6    1 = resets FREEZE-mode (turns back to normal mode)
        5    1 = enable RAM at ROML ($8000-$9FFF) &
                 I/O-2 ($DF00-$DFFF = $9F00-$9FFF)
        4    ROM bank selector high (A14)
        3    ROM bank selector low  (A13)
        2    1 = disable cartridge (turn off $DE00)
        1    1 = /EXROM high
        0    1 = /GAME low

Additionally the RAM or ROM can be available through a window in the I/O-2 range.

#### 16.11.3.3 2 - KCS Power Cartridge

Size | 16Kb (2 banks of 8K each)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | module #1 - $8000-9FFF module #2 - $A000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 20 01 00 00 02 00 00 00 00 00 00 00 00   ????????????????
    0020: 4B 43 53 20 50 6F 77 65 72 20 43 61 72 74 72 69   KCS?Power?Cartri
    0030: 64 67 65 00 00 00 00 00 00 00 00 00 00 00 00 00   dge?????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0050: 09 80 5E FE C3 C2 CD 38 30 78 D8 A2 FF 9A A9 27   ?.^....80x..?..'
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 00 A0 00 20 00   CHIP???????? ???
    2060: 97 E3 16 A1 FF FF FF 20 13 A0 A5 01 09 01 85 01   .?.????? ¥????

#### 16.11.3.4 3 - Final Cartridge III

Size | 64Kb (4 banks of 16Kb each)
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $8000-BFFF (all modules)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 03 01 01 00 00 00 00 00 00   ???@????????????
    0020: 46 69 6E 61 6C 20 43 61 72 74 72 69 64 67 65 20   Final?Cartridge?
    0030: 49 49 49 20 31 39 38 37 00 00 00 00 00 00 00 00   III?1987????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00   CHIP??@?????.?@?
    0050: 09 80 5E FE C3 C2 CD 38 30 4C 4C 80 4C 55 95 4C   ?.^....80LL.LUL
    ...
    4050: 43 48 49 50 00 00 40 10 00 00 00 01 80 00 40 00   CHIP??@?????.?@?
    4060: 01 02 00 81 5D 81 61 81 99 81 D8 81 0B 82 33 82   ???]a.?3
    ...
    8060: 43 48 49 50 00 00 40 10 00 00 00 02 80 00 40 00   CHIP??@?????.?@?
    8070: 20 43 80 20 52 80 A9 4E 20 05 DE 20 FD BF AD 39   ?C.?R..N??.?..9
    ...
    C070: 43 48 49 50 00 00 40 10 00 00 00 03 80 00 40 00   CHIP??@?????.?@?
    C080: A2 06 BD DD 85 95 05 CA 10 F8 AE A0 02 E8 EC A2   .??.?.??® ???.

A total of 64 kB of ROM memory is organized into four $4000 banks located at $8000-$BFFF.

The banks are arranged in the following way:

        Bank 0:  BASIC, Monitor, Disk-Turbo
        Bank 1:  Notepad, BASIC (Menu Bar)
        Bank 2:  Desktop, Freezer/Print
        Bank 3:  Freezer, Compression

The cartridges uses the entire I/O-1 and I/O-2 range. Bank switching is done by writing the bank number plus $40 into memory location $DFFF. For instance, to select bank 2, $DFFF is set to $42.

The CRT file contains four CHIP blocks, each block with a start address of $8000, length $4000 and the bank number in the bank field. In the cartridge header, both EXROM ($18) and GAME ($19) are set to 1 to enable the 16 kB ROM configuration.

The registers are arranged in the following way:

One register at $DFFF:

        bit  meaning
        ---  -------
        7      Hide this register (1 = hidden)
        6      NMI line  (0 = low = active) *1)
        5      GAME line  (0 = low = active) *2)
        4      EXROM line (0 = low = active)
        2-3    unassigned (usually set to 0)
        0-1    number of bank to show at $8000

1) if either the freezer button is pressed, or bit 6 is 0, then an NMI is generated

2) if the freezer button is pressed, GAME is also forced low

The rest of I/O-1/I/O-2 contain a mirror of the last 2 pages of the currently selected ROM bank (also at $dfff, contrary to what some other documents say)

#### 16.11.3.5 4 - Simons' Basic

Size | 16Kb (2 banks of 8kb each)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | module #1 - $8000-9FFF module #2 - $A000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 04 00 01 00 00 00 00 00 00   ???@????????????
    0020: 53 69 6D 6F 6E 27 73 20 42 61 73 69 63 00 00 00   Simon's?Basic???
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0050: 52 81 52 81 C3 C2 CD 38 30 41 4C 52 81 20 2C 81   RR...80ALR?,
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 00 A0 00 20 00   CHIP???????? ???
    2060: 20 A4 A6 99 9E CB A0 05 A5 A8 91 20 A4 A6 99 A2   ???. ?¥?.???.

Simons' BASIC permanently uses 16 kB ($4000) bytes of cartridge memory from $8000-$BFFF. However, through some custom bank-switching logic the upper area ($A000-$BFFF) may be disabled so Simons' BASIC may use it as additional RAM. Writing a value of $01 to address location $DE00 banks in ROM, $00 disables ROM and enables RAM.

The CRT file contains two CHIP blocks of length $2000 each, the first block having a start address of $8000, the second block $A000. In the cartridge header, EXROM ($18) is set to 0, GAME ($19) is set to 1 to indicate the RESET/power-up configuration of 8 kB ROM.

#### 16.11.3.6 5 - Ocean type 1

Size | 32Kb, 128Kb, 256Kb or 512Kb sizes (4, 16, 32 or 64 banks of 8Kb)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | Banks 00-15 - $8000-9FFF Banks 16-31 - $A000-BFFF (except Terminator 2)

           00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
           -----------------------------------------------   ----------------
    00000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    00010: 00 00 00 40 01 00 00 05 00 00 00 00 00 00 00 00   ???@????????????
    00020: 53 48 41 44 4F 57 20 4F 46 20 54 48 45 20 42 45   SHADOW?OF?THE?BE
    00030: 41 53 54 00 00 00 00 00 00 00 00 00 00 00 00 00   AST?????????????
    00040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    00050: 09 80 83 81 C3 C2 CD 38 30 4C 83 81 4C 76 82 80   ?....80LLv.
     ...
    02050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00   CHIP????????.???
    02060: 59 6D 00 56 AD 00 55 AE F0 00 01 A0 FE 00 01 F8   Ym?V?U®??? .???
     ...
    20140: 43 48 49 50 00 00 20 10 00 00 00 10 A0 00 20 00   CHIP???????? ???
    20150: 0A 9A 55 FF 9B 69 57 FE AA 65 96 FE 65 0F D6 D9   ?.U?iW.×e.e?..

Here is a list of the known OCEAN cartridges:

        Batman The Movie    (128 kB)
        Battle Command      (128 kB)
        Double Dragon       (128 kB)
        Navy Seals          (128 kB)
        Pang                (128 kB)
        Robocop 3           (128 kB)
        Space Gun           (128 kB)
        Toki                (128 kB)
        Chase H.Q. II       (256 kB)
        Robocop 2           (256 kB)
        Shadow of the Beast (256 kB)
        Terminator 2        (512 kB)

The 32Kb type of cart has 4 banks of 8Kb ($2000), banked in at $8000-$9FFF.

The 128Kb type of cart has 16 banks of 8Kb ($2000), banked in at $8000-$9FFF.

The 256Kb type of cart has 32 banks of 8Kb ($2000), 16 banked in at $8000-$9FFF, and 16 banked in at $A000-$BFFF.

The 512Kb type of cart has 64 banks of 8Kb ($2000), banked in at $8000-$9FFF.

Bank switching is done by writing to $DE00. The lower six bits give the bank number (ranging from 0-63). Bit 7 in this selection word is always set.

#### 16.11.3.7 6 - Expert Cartridge

Size | 8Kb
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 06 01 01 00 00 00 00 00 00   ???@????????????
    0020: 45 78 70 65 72 74 20 43 61 72 74 72 69 64 67 65   Expert?Cartridge
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 40 10 00 02 00 00 80 00 20 00   CHIP??@?????.???
    0050: 00 00 00 0A F3 00 00 00 00 00 00 00 00 00 00 00   ????????????????

#### 16.11.3.8 7 - Fun Play, Power Play

Size | 128Kb (16 banks of 8Kb modules)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $8000-9FFF (all modules)

           00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
           -----------------------------------------------   ----------------
    00000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    00010: 00 00 00 40 01 00 00 07 00 00 00 00 00 00 00 00   ???@????????????
    00020: 46 55 4E 20 50 4C 41 59 00 00 00 00 00 00 00 00   FUN?PLAY????????
    00030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    00040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    00050: 1E 80 86 EA C3 C2 CD 38 30 1B 00 81 0D 08 80 00   ?.....80????.?
     ...
    02050: 43 48 49 50 00 00 20 10 00 00 00 08 80 00 20 00   CHIP????????.???
    02060: 78 A2 F0 86 01 BD 1D 08 9D F8 00 CA D0 F7 4C 00   x.???????..?L?
     ...
    04060: 43 48 49 50 00 00 20 10 00 00 00 10 80 00 20 00   CHIP????????.???
    04070: 38 E5 68 85 03 B0 11 27 03 12 C0 18 69 27 42 90   8?h?°?'??.?i'B
     ...
    06070: 43 48 49 50 00 00 20 10 00 00 00 18 80 00 20 00   CHIP????????.???
    06080: 44 D0 5E 06 02 C0 44 11 40 04 11 44 01 5F 1C 73   D.^??.D?@??D?_?s
     ...
    1E130: 43 48 49 50 00 00 20 10 00 00 00 39 80 00 20 00   CHIP???????9.???
    1E140: 85 EB 41 EA 9E 08 03 00 C0 06 18 01 00 C0 08 03   ?A.???.????.??

The FUN PLAY Cartridge uses $DE00 for bank selection, and uses 8Kb banks ($2000) at $8000-$9FFF. There are 16 banks of ROM memory and are referenced by the following values:

        $00 -> Bank 0
        $08 -> Bank 1
        $10 -> Bank 2
        $18 -> Bank 3
        $20 -> Bank 4
        $28 -> Bank 5
        $30 -> Bank 6
        $38 -> Bank 7
        $01 -> Bank 8
        $09 -> Bank 9
        $11 -> Bank 10
        $19 -> Bank 11
        $21 -> Bank 12
        $29 -> Bank 13
        $31 -> Bank 14
        $39 -> Bank 15

The bank field in the chip headers is set according to the value written to $DE00. The following bits are used for bank decoding in $DE00 (0 being the LSB, 3 being the MSB).

            Bit# 76543210
                 xx210xx3

After copying memory from the ROM banks, the selection program writes a value of $86 to $DE00. This seems either to reset or disable the cartridge ROM.

#### 16.11.3.9 8 - Super Games

Size | 64Kb (4 banks of 16Kb each)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Startup mode | 16k game
Load address | $8000-BFFF (all modules)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 08 00 00 00 00 00 00 00 00   ???@????????????
    0020: 53 55 50 45 52 20 47 41 4D 45 53 00 00 00 00 00   SUPER?GAMES?????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00   CHIP??@?????.?@?
    0050: 0A 80 0A 80 C3 C2 CD 38 30 00 A9 80 A0 00 85 FB   ?.?....80?.. ?.
    ...
    4050: 43 48 49 50 00 00 40 10 00 00 00 01 80 00 40 00   CHIP??@?????.?@?
    4060: 27 80 A8 80 C3 C2 CD 38 30 00 40 C0 40 C0 40 C0   '.?....80?@.@.@.
    ...
    8060: 43 48 49 50 00 00 40 10 00 00 00 02 80 00 40 00   CHIP??@?????.?@?
    8070: 00 00 00 49 4D C7 64 47 46 45 F3 48 DC 08 7E 0B   ???IM.dGFE?H.?~?
    ...
    C070: 43 48 49 50 00 00 40 10 00 00 00 03 80 00 40 00   CHIP??@?????.?@?
    C080: D5 F9 F0 C1 D5 F7 F0 BD E8 B5 02 F0 FB C9 05 30   .??..????µ??..?0

The Super Games cartridge uses 4 16Kb banks ($8000-$BFFF) of ROM memory. Bank selecting is done by writing to $DF00.

$DF00 register is as follows:

        bit   meaning
        ---   -------
         0    bank bit 0
         1    bank bit 1
         2    mode (0 = EXROM/GAME (bridged on the same wire - 16k config) 1 = cartridge disabled)
         3    write-protect-latch  (1 = no more changes are possible until the next hardware-reset )
        4-7   unused

#### 16.11.3.10 9 - Atomic Power

Size | 32Kb (4 banks of 8Kb modules)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $8000-9FFF (all modules)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 09 00 00 00 00 00 00 00 00   ???@????????????
    0020: 41 74 6F 6D 69 63 20 50 6F 77 65 72 00 00 00 00   Atomic?Power????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0050: 09 80 0C 80 C3 C2 CD 38 30 4C 41 80 4C 1E 80 4C   ?.?....80LA.L?.L
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00   CHIP????????.???
    2060: 09 80 0C 80 C3 C2 CD 38 30 4C 3F 80 4C 91 80 4C   ?.?....80L?.L..L
    ...
    4060: 43 48 49 50 00 00 20 10 00 00 00 02 80 00 20 00   CHIP????????.???
    4070: EF FC 09 80 C3 C2 CD 38 30 4C 27 80 4C DB 81 4C   ?.?....80L'.L.L
    ...
    6070: 43 48 49 50 00 00 20 10 00 00 00 03 80 00 20 00   CHIP????????.???
    6080: 09 80 0C 80 C3 C2 CD 38 30 4C 73 86 4C 30 80 4C   ?.?....80LsL0.L

This cart has 32Kb of ROM and 8Kb of RAM

Writing to I/O-1 will do the following:

        bit  meaning
        ---  -------
        7    extra ROM bank selector (A15) (unused)
        6    1 = resets FREEZE-mode (turns back to normal mode)
        5    1 = enable RAM at ROML ($8000-$9FFF) &
                 I/O-2 ($DF00-$DFFF = $9F00-$9FFF)
        4    ROM bank selector high (A14)
        3    ROM bank selector low  (A13)
        2    1 = disable cartridge (turn off $DE00)
        1    1 = /EXROM high
        0    1 = /GAME low

If bit 5 (RAM enable) is 1, bit 0,1 (exrom/game) is == 2 (cart off), bit 2,6,7 (cart disable, freeze clear) are 0, then cart ROM (Bank 0..3) is mapped at 8000-9FFF, and cart RAM (Bank 0) is mapped at A000-BFFF and cart RAM (Bank 0) is is enabled in the I/O-2 area using 16Kb game config.

The cart RAM or ROM is available through a window in the I/O-2 range.

#### 16.11.3.11 10 - Epyx Fastload

Size | 8Kb
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 0A 01 01 00 00 00 00 00 00   ???@????????????
    0020: 45 50 59 58 20 46 41 53 54 4C 4F 41 44 00 00 00   EPYX?FASTLOAD???
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0050: 30 80 5E FE C3 C2 CD 38 30 20 04 90 4C 38 DF AB   0.^....80??L8?«

The Epyx FastLoad cart uses a simple capacitor to toggle the ROM on and off:

the capacitor is discharged, and 8k game config enabled, by either reading ROML or reading I/O-1. If none of those accesses happen the capacitor will charge, and if it is charged (after 512 cycles) then the ROM will get disabled.

#### 16.11.3.12 11 - Westermann Learning

Size | 16Kb
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $8000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 0B 00 00 00 00 00 00 00 00   ???@????????????
    0020: 57 45 53 54 45 52 4D 41 4E 4E 00 00 00 00 00 00   WESTERMANN??????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 40 00   CHIP????????.?@?
    0050: 09 80 9C 80 C3 C2 CD 38 30 A2 00 8E 16 D0 20 84   ?.....80.??.?

Any read from the I/O-2 range will switch the cart off.

#### 16.11.3.13 12 - Rex Utility

Size | 8K
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 0C 00 01 00 00 00 00 00 00   ???@????????????
    0020: 52 45 58 00 00 00 00 00 00 00 00 00 00 00 00 00   REX?????????????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00   CHIP????????.???
    0050: 08 80 C1 FE C3 C2 CD 38 30 6C 95 E3 20 A3 FD 20   ?......80l.?£.?

Reading from $DF00-DFBF disables ROM, reading from $DFC0-DFFF enables ROM (8k game config).

#### 16.11.3.14 13 - Final Cartridge I

Size | 16Kb
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $8000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
          -----------------------------------------------   ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20   C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 0D 01 01 00 00 00 00 00 00   ???@????????????
    0020: 54 68 65 20 46 69 6E 61 6C 20 43 61 72 74 72 69   The?Final?Cartri
    0030: 64 67 65 20 49 00 00 00 00 00 00 00 00 00 00 00   dge?I???????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00   CHIP??@?????.?@?
    0050: 80 BA 5E FE C3 C2 CD 38 30 00 A0 A0 20 2D FE 58   .÷^....80?  ?-.X

Any access to I/O-1 turns cartridge ROM off. Any access to I/O-2 turns cartridge ROM on.

The cart ROM is visible in I/O-1 and I/O-2.

#### 16.11.3.15 14 - Magic Formel

Size | 64Kb (8 banks of 8Kb)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load Address | $E000-FFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 0E 01 01 00 00 00 00 00 00  ???@????????????
    0020: 4D 61 67 69 63 20 46 6F 72 6D 65 6C 00 00 00 00  Magic?Formel????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 E0 00 20 00  CHIP????????????
    0050: 4D 46 30 8D 00 DF 60 8D 01 DF 60 8D 02 DF 60 8D  MF0??`??`??`
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 E0 00 20 00  CHIP????????????
    2060: 4C 5F E4 8D 00 DF 60 8D 01 DF 60 8D 02 DF 60 8D  L_???`??`??`
    ...
    4060: 43 48 49 50 00 00 20 10 00 00 00 02 E0 00 20 00  CHIP????????????
    4070: 4D 46 32 8D 00 DF 60 8D 01 DF 60 8D 02 DF 60 8D  MF2??`??`??`
    ...
    6070: 43 48 49 50 00 00 20 10 00 00 00 03 E0 00 20 00  CHIP????????????
    6080: 4D 46 33 8D 00 DF 60 8D 01 DF 60 8D 02 DF 60 8D  MF3??`??`??`
    ...
    8080: 43 48 49 50 00 00 20 10 00 00 00 04 E0 00 20 00  CHIP????????????
    8090: 4D 46 34 8D 00 DF 60 8D 01 DF 60 8D 02 DF 60 8D  MF4??`??`??`
    ...
    A090: 43 48 49 50 00 00 20 10 00 00 00 05 E0 00 20 00  CHIP????????????
    A0A0: 4D 46 35 8D 00 DF 60 8D 01 DF 60 8D 02 DF 60 8D  MF5??`??`??`
    ...
    C0A0: 43 48 49 50 00 00 20 10 00 00 00 06 E0 00 20 00  CHIP????????????
    C0B0: 4D 46 36 8D 00 DF 60 8D 01 DF 60 8D 02 DF 60 8D  MF6??`??`??`
    ..
    E0B0: 43 48 49 50 00 00 20 10 00 00 00 07 E0 00 20 00  CHIP????????????
    E0C0: 4D 46 37 8D 00 DF 60 8D 01 DF 60 8D 02 DF 60 8D  MF7??`??`??`

#### 16.11.3.16 15 - C64 Game System, System 3

Size | 512Kb (64 banks of 8Kb each)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $8000-9FFF (all modules)

            00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
            -----------------------------------------------  ----------------
    000000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    000010: 00 00 00 40 01 00 00 0F 00 01 00 00 00 00 00 00  ???@????????????
    000020: 43 36 34 47 53 20 43 61 72 74 72 69 64 67 65 00  C64GS?Cartridge?
    000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    000040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    000050: 6D 80 C5 80 C3 C2 CD 38 30 4C CB 80 4C 36 84 4C  m......80L..L6L
    ...
    002050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    002060: 18 D0 A9 FF 8D 15 D0 8D 1D D0 8D 17 D0 A2 07 A9  ?..??.?.?..?.
    ...
    004060: 43 48 49 50 00 00 20 10 00 00 00 02 80 00 20 00  CHIP????????.???
    004070: E0 08 19 21 77 84 52 98 9F 80 A5 21 31 01 31 89  ???!wR.¥!1?1
    ...
    006070: 43 48 49 50 00 00 20 10 00 00 00 03 80 00 20 00  CHIP????????.???
    006080: C0 08 1C 1D A0 92 03 03 D8 AA 04 C0 B8 01 40 EA  .??? .??.×?.??@.
    ...
    07E430: 43 48 49 50 00 00 20 10 00 00 00 3F 80 00 20 00  CHIP????????.???
    07E440: 45 20 41 20 42 49 47 20 58 FE 4F 4E 20 54 48 49  E?A?BIG?X.ON?THI

Here is a list of the known cartridges:

        C64GS 4-in-1      (Commodore)  (512 kB)
        Last Ninja Remix  (System 3)   (512 kB)
        Myth              (System 3)   (512 kB)

ROM memory is organized in 8Kb ($2000) banks located at $8000-$9FFF. Bank switching is done by writing to address $DE00+X, where X is the bank number (STA $DE00,X). For instance, to read from bank 3, address $DE03 is written to. Reading from anywhere in the I/O-1 range will disable the cart.

The CRT file contains a string of CHIP blocks, each block with a start address of $8000, length $2000 and the bank number in the bank field. In the cartridge header, EXROM ($18) is set to 0, GAME ($19) is set to 1 to enable the 8 kB ROM configuration.

#### 16.11.3.17 16 - Warp Speed

Size | 16Kb
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $8000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 10 01 01 00 00 00 00 00 00  ???@????????????
    0020: 57 61 72 70 73 70 65 65 64 00 00 00 00 00 00 00  Warpspeed???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00  CHIP??@?????.?@?
    0050: 4C 22 80 4C 22 80 FF 43 42 4D 20 53 E4 20 18 E5  L".L".?CBM?S????

After RESET or POWER ON, 16kB of cartridge ROM is visible at $8000-$BFFF. Additionally, ROM normally located at $9E00-$9FFF is mirrored into I/O-1 and I/O-2 at $DE00-$DFFF. ROM at $8000-$BFFF is disabled by writing into the I/O-2 area (typically $DF00) and may be re-enabled by writing into I/O-1 ($DE00). However, the $DE00-$DFFF (I/O-1/I/O-2) area itself always remains mapped to cartridge ROM.

#### 16.11.3.18 17 - Dinamic

Size | 128Kb (16 banks of 8Kb each)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $8000-9FFF (all modules)

            00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
            -----------------------------------------------  ----------------
    000000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    000010: 00 00 00 40 01 00 00 11 00 01 00 00 00 00 00 00  ???@????????????
    000020: 4E 61 72 63 6F 20 50 6F 6C 69 63 65 00 00 00 00  Narco?Police????
    000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    000040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    000050: 0B 80 0B 80 C3 C2 CD 38 30 00 00 78 A2 FF 9A D8  ?.?....80??x.?..
    ..
    002050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    002060: 1C 8C 1B 8C 16 16 8F 16 16 88 1C 1C 86 1C 1C 89  ??????????
    ..
    004060: 43 48 49 50 00 00 20 10 00 00 00 02 80 00 20 00  CHIP????????.???
    004070: B6 02 07 08 07 07 00 0A 0A B6 00 05 0A 00 07 07  ¶????????¶??????
    ..
    01E130: 43 48 49 50 00 00 20 10 00 00 00 0F 80 00 20 00  CHIP????????.???
    01E140: 00 D5 70 03 F5 70 0F 5F 70 0F F7 70 35 FD F0 37  ?.p??p?_p??p5.?7

Here is a list of the known DINAMIC cartridges:

        Narco Police  (128 kB)
        Satan         (128 kB)

ROM memory is organized in 8Kb ($2000) banks located at $8000-$9FFF. Bank switching is done by reading from address $DE00+X, where X is the bank number (LDA $DE00,X). For instance, to read from bank 3, address $DE03 is accessed.

The CRT file contains a string of CHIP blocks, each block with a start address of $8000, length $2000 and the bank number in the bank field. In the cartridge header, EXROM ($18) is set to 0, GAME ($19) is set to 1 to enable the 8 kB ROM configuration.

#### 16.11.3.19 18 - Zaxxon, Super Zaxxon (SEGA)

Size | 20Kb (3 banks of different sizes)
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $8000-8FFF (mirrored in $9000-9FFF, module 0, chip U1) $A000-BFFF (banked modules 1 and 2, chip U2)

            00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
            -----------------------------------------------  ----------------
    000000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    000010: 00 00 00 40 01 00 00 12 00 00 00 00 00 00 00 00  ???@????????????
    000020: 5A 61 78 78 6F 6E 00 00 00 00 00 00 00 00 00 00  Zaxxon??????????
    000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    000040: 43 48 49 50 00 00 10 10 00 00 00 00 80 00 10 00  CHIP????????.???
    000050: 0D 80 29 80 C3 C2 CD 38 30 78 4C 09 80 78 A9 00  ?.)....80xL?.x.?
    ..
    001050: 43 48 49 50 00 00 20 10 00 00 00 00 A0 00 20 00  CHIP???????? ???
    001060: A2 0F BD 00 20 D0 04 CA 10 F8 60 BD 70 20 F0 0D  .????.?.??`?p???
    ..
    003060: 43 48 49 50 00 00 20 10 00 00 00 01 A0 00 20 00  CHIP???????? ???
    003070: 65 A2 36 A3 E7 A3 CB A4 94 A5 86 A6 5E A7 35 A8  e.6£?£.?¥?^§5?

The (Super) Zaxxon carts use a 4Kb ($1000) ROM at $8000-$8FFF (mirrored in $9000-$9FFF) along with two 8Kb ($2000) cartridge banks located at $A000-$BFFF. One of the two banks is selected by doing a read access to either the $8000-$8FFF area (bank 0 is selected) or to $9000-$9FFF area (bank 1 is selected). EXROM ($18 = $00) and GAME ($19 = $00) lines are always pulled to GND to select the 16 kB ROM configuration.

The CRT file includes three CHIP blocks:

        a) bank = 0, load address = $8000, size = $1000
        b) bank = 0, load address = $A000, size = $2000
        c) bank = 1, load address = $A000, size = $2000

#### 16.11.3.20 19 - Magic Desk, Domark, HES Australia

Size | 32Kb, 64Kb or 128Kb sizes (4 to 16 banks of 8Kb each)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Startup mode | 8k Game
Load address | (banks 00-15) - $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 13 00 01 00 00 00 00 00 00  ???@????????????
    0020: 4D 61 67 69 63 20 44 65 73 6B 00 00 00 00 00 00  Magic?Desk??????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 09 80 C6 CA C3 C2 CD 38 30 8E 16 D0 20 A3 FD 20  ?......80?.?£.?
    ..
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    2060: 00 3F 0A 01 00 86 4E 24 28 31 30 29 3A 4A 4F 59  ?????N$(10):JOY
    ..
    4060: 43 48 49 50 00 00 20 10 00 00 00 02 80 00 20 00  CHIP????????.???
    4070: 00 8B C9 28 4E 24 2C 31 29 B3 B1 22 FF 22 A7 32  ?.(N$,1)³±"?"§2
    ..
    6070: 43 48 49 50 00 00 20 10 00 00 00 03 80 00 20 00  CHIP????????.???
    6080: AE 01 83 33 2C 37 2C 22 32 29 20 44 45 4C 20 4B  ®?3,7,"2)?DEL?K

This cartridge type is very similar to the OCEAN cart type: ROM memory is organized in 8Kb ($2000) banks located at $8000-$9FFF. Bank switching is done by writing the bank number to $DE00. Deviant from the Ocean type, bit 7 is cleared for selecting one of the ROM banks. If bit 7 is set ($DE00 = $80), the GAME/EXROM lines are disabled, turning on RAM at $8000-$9FFF instead of ROM.

In the cartridge header, EXROM ($18) is set to 0, GAME ($19) is set to 1 to indicate the RESET/power-up configuration of 8 kB ROM.

Here is a list of the known cartridges:

        Ghosbusters        (HES Australia)   (32 kB)
        Magic Desk         (Commodore)       (32 kB)
        Badlands           (Domark)          (64 kB)
        Vindicators        (Domark)          (64 kB)
        Wonderboy          (HES Australia)   (64 kB)
        Cyberball          (Domark)         (128 kB)

#### 16.11.3.21 20 - Super Snapshot V5

Size | 64Kb (4 banks of 16Kb each)
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $8000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 14 01 01 00 00 00 00 00 00  ???@????????????
    0020: 53 75 70 65 72 20 53 6E 61 70 73 68 6F 74 20 35  Super?Snapshot?5
    0030: 20 4E 54 53 43 00 00 00 00 00 00 00 00 00 00 00  ?NTSC???????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00  CHIP??@?????.?@?
    0050: 09 80 59 80 C3 C2 CD 38 30 20 03 9F 00 FA F4 20  ?.Y....80??????
    ...
    4050: 43 48 49 50 00 00 40 10 00 00 00 01 80 00 40 00  CHIP??@?????.?@?
    4060: 79 DE BC FE C3 C2 CD 38 30 A9 05 8D 20 D0 8D 21  y.?....80.??.!
    ...
    8060: 43 48 49 50 00 00 40 10 00 00 00 02 80 00 40 00  CHIP??@?????.?@?
    8070: 50 DE BC FE C3 C2 CD 38 30 A9 0A 85 6A A9 0D 85  P.?....80.?j.?
    ...
    C070: 43 48 49 50 00 00 40 10 00 00 00 03 80 00 40 00  CHIP??@?????.?@?
    C080: 50 DE BC FE C3 C2 CD 38 30 85 07 20 1A AD A5 76  P.?....80???¥v

The first page of the currently selected ROM bank is mirrored in the I/O-1 range when reading.

The control Register is the I/O-1 range when writing:

        bit  meaning
        ---  -------
        7-5  unused
        4    ROM/RAM bank bit 1
        3    ROM enable
        2    ROM/RAM bank bit 0
        1    RAM enable, EXROM
        0    release freeze, !GAME

#### 16.11.3.22 21 - Comal-80

Size | 64Kb (4 banks of 16Kb each)
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $8000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 15 01 01 00 00 00 00 00 00  ???@????????????
    0020: 43 6F 6D 61 6C 20 38 30 00 00 00 00 00 00 00 00  Comal?80????????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00  CHIP??@?????.?@?
    0050: 87 87 70 CF C3 C2 CD 38 30 4C AA CF 4C 70 CF 4C  ..p....80L×.Lp.L
    ...
    4050: 43 48 49 50 00 00 40 10 00 00 00 01 80 00 40 00  CHIP??@?????.?@?
    4060: AA CF 70 CF C3 C2 CD 38 30 01 29 01 28 01 2C 04  ×.p....80?)?(?,?
    ...
    8060: 43 48 49 50 00 00 40 10 00 00 00 02 80 00 40 00  CHIP??@?????.?@?
    8070: AA CF 70 CF C3 C2 CD 38 30 91 92 92 92 92 92 92  ×.p....80.......
    ...
    C070: 43 48 49 50 00 00 40 10 00 00 00 03 80 00 40 00  CHIP??@?????.?@?
    C080: 7B C8 7E C8 C3 C2 CD 38 30 43 4F 4D 41 4C 80 93  ..~....80COMAL..

The Comal-80 Cartridge uses $DE00 for bank selection, and uses 16Kb banks ($4000) at $8000-$BFFF. There are 4 banks of ROM memory and are referenced by the following values:

           $80 -> Bank 0
           $81 -> Bank 1
           $82 -> Bank 2
           $83 -> Bank 3

#### 16.11.3.23 22 - Structured Basic

Size | 16Kb (2 banks of 8Kb each)
EXROM | inactive (hi) (1)
GAME | active (0)
Load address | $8000-9FFF

No sample data/file available.

Any read/write access to $DE00 or $DE01 will switch in bank 0. Any read/write access to $DE02 will switch in bank 1. Any read/write access to $DE03 will switch off EXROM.

#### 16.11.3.24 23 - Ross

Size | 16Kb or 32Kb sizes (1 or 2 banks of 16Kb each)
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $8000-BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 17 00 00 00 00 00 00 00 00  ???@????????????
    0020: 52 6F 73 73 20 31 34 00 00 00 00 00 00 00 00 00  Ross?14?????????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00  CHIP??@?????.?@?
    0050: 09 80 09 80 C3 C2 CD 38 30 A2 00 BD 20 80 4D 0E  ?.?....80.???.M?
    ...
    4050: 43 48 49 50 00 00 40 10 00 00 00 01 80 00 40 00  CHIP??@?????.?@?
    4060: 3F 5A 4D 4D 50 4D 8D 25 3F 1A 1F 77 3F CD E0 3F  ?ZMMPM%???w?.??

Any read access to $DE00 will switch in bank 1 (if cart is 32Kb). Any read access to $DF00 will switch off EXROM and GAME.

#### 16.11.3.25 24 - Dela EP64

Size | 8Kb to 72kb sizes (1 to 9 banks of 8Kb each, or 1 bank of 8Kb and 1 or 2 banks of 32Kb each)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 18 00 01 00 00 00 00 00 00  ???@????????????
    0020: 44 45 4C 41 20 45 50 36 34 00 00 00 00 00 00 00  DELA?EP64???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 00 85 5E FE C3 C2 CD 38 30 FF FF FF FF FF FF FF  ?^....80???????
    ...
    2050: 43 48 49 50 00 00 80 10 00 00 00 01 80 00 80 00  CHIP??.?????.?.?
    2060: 54 45 53 54 0D 2A 0D 54 45 20 36 34 0D 00 00 00  TEST?*?TE?64????

This is an eprom cartridge. It has 1 2764 (8Kb) which holds the base eprom with the base menu, and 2 27256 eproms of which 8Kb parts are banked into the $8000-9FFF area.

The bank selecting is done by writing to $DE00. The following bits are used for bank decoding in $DE00 (0 being the LSB, 3 being the MSB).

             Bit# 76543210
                  xx10xx32

Any bank value below 4 or above 11 switches in the base bank (bank 0).

The bit values for each eprom bank are :

        eprom bank 1 : xx00xx01
        eprom bank 2 : xx01xx01
        eprom bank 3 : xx10xx01
        eprom bank 4 : xx11xx01
        eprom bank 5 : xx00xx10
        eprom bank 6 : xx01xx10
        eprom bank 7 : xx10xx10
        eprom bank 8 : xx11xx10

Setting bit 7 high will switch off EXROM.

#### 16.11.3.26 25 - Dela EP7x8

Size | 8Kb to 64kb sizes (1 to 8 banks of 8Kb each)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 19 00 01 00 00 00 00 00 00  ???@????????????
    0020: 44 45 4C 41 20 45 50 37 78 38 00 00 00 00 00 00  DELA?EP7x8??????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 09 80 5E FE C3 C2 CD 38 30 78 A2 FF 9A D8 8E 16  ?.^....80x.?..?
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    2060: 94 83 A0 83 C3 C2 CD 38 30 02 BB 5A 30 5F EE 3D   ...80?»Z0_?=

This is an eprom cartridge. It has 8 8Kb banks of which the first holds the base menu, the other eproms can be banked into the $8000-9FFF area.

The bank selecting is done by writing to $DE00. Each low bit is used to bank in the respective eprom. If all bits are high then the EXROM is switched off.

The bit values for each eprom bank is:

        eprom bank 1 : 11111110 ($FE) (base eprom)
        eprom bank 2 : 11111101 ($FD)
        eprom bank 3 : 11111011 ($FB)
        eprom bank 4 : 11110111 ($F7)
        eprom bank 5 : 11101111 ($EF)
        eprom bank 6 : 11011111 ($DF)
        eprom bank 7 : 10111111 ($BF)
        eprom bank 8 : 01111111 ($7F)

        EXROM off    : 11111111 ($FF)

#### 16.11.3.27 26 - Dela EP256

Size | 8Kb to 262kb sizes (1 to 33 banks of 8Kb each)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 1A 00 01 00 00 00 00 00 00  ???@????????????
    0020: 44 45 4C 41 20 45 50 32 35 36 00 00 00 00 00 00  DELA?EP256??????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 00 85 5E FE C3 C2 CD 38 30 93 0D 2B 2B 2B 20 45  ?^....80.?+++?E
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    2060: 09 80 28 80 C3 C2 CD 38 30 78 A2 05 8E 16 D0 20  ?.(....80x.??.?
    ...
    4060: 43 48 49 50 00 00 20 10 00 00 00 02 80 00 20 00  CHIP????????.???
    4070: 0B 80 BC FE C3 C2 CD 38 30 DC 10 8E 16 D0 20 87  ?.?....80.??.?.
    ...
    6070: 43 48 49 50 00 00 20 10 00 00 00 03 80 00 20 00  CHIP????????.???
    6080: 09 80 F6 8E C3 C2 CD 38 30 A2 C8 8E 16 D0 20 ..  ?.?...80..?.?.
    ...
    8080: 43 48 49 50 00 00 20 10 00 00 00 04 80 00 20 00  CHIP????????.???
    8090: 94 83 A0 83 C3 C2 CD 38 30 02 BB 5A 30 5F EE 3D   ...80?»Z0_?=

This is an eprom cartridge. It has 33 8Kb banks of which the first holds the base menu, the other eproms can be banked into the $8000-9FFF area.

The bank selecting is done by writing to $DE00.

The values for the (extra) eprom banks are:

        eprom banks  1- 8 : $38-3F
        eprom banks  9-16 : $28-2F
        eprom banks 17-24 : $18-1F
        eprom banks 25-32 : $08-0F

Setting bit 7 high will switch off EXROM.

#### 16.11.3.28 27 - Rex EP256

Size | 8Kb to 262kb sizes (1 bank of 8Kb and 1 to 8 banks of either 8Kb, 16Kb or 32Kb)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 1B 00 01 00 00 00 00 00 00  ???@????????????
    0020: 52 45 58 20 45 50 32 35 36 00 00 00 00 00 00 00  REX?EP256???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 09 80 C1 FE C3 C2 CD 38 30 20 A3 FD 20 50 FD 20  ?......80?£.?P.?
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    2060: 09 80 F2 8F C3 C2 CD 38 30 A2 C8 8E 16 D0 20 A3  ?.?...80..?.?£
    ...
    4060: 43 48 49 50 00 00 40 10 00 00 00 02 80 00 40 00  CHIP??@?????.?@?
    4070: 09 80 09 80 C3 C2 CD 38 30 58 D8 20 84 FF 20 8A  ?.?....80X.???

This is an eprom cartridge. It has 9 eprom sockets, of which the first holds the base eprom with the base menu which is an 8Kb eprom, the other eprom sockets can handle 8Kb, 16Kb or 32Kb eproms, of which 8kb can be banked into the $8000-9FFF area.

The bank selecting is done by writing to $DFA0. Bits 2, 1 and 0 determine which socket is used and bits 5 and 4 are used to select an 8Kb piece of the eprom.

The possible values for bits 5 and 4 for the (extra) eprom banks are:

         8Kb        : 3, 2, 1, 0

        16Kb bank 0 : 2, 0
        16Kb bank 1 : 3, 1

        32Kb bank 0 : 0
        32Kb bank 1 : 1
        32Kb bank 2 : 2
        32Kb bank 3 : 3

Reading from $DFC0 switches off the EXROM. Reading from $DFE0 switches on the EXROM.

#### 16.11.3.29 28 - Mikro Assembler

Size | 8Kb (1 bank of 8Kb)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $8000-9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 1C 00 01 00 00 00 00 00 00  ???@????????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 60 80 FE 80 C3 C2 CD 38 30 4C 07 87 4C CA 82 41  `......80L?.L.A

The $9E00-$9EFF range is mirrored at $DE00-$DEFF. The $9F00-$9FFF range is mirrored at $DF00-$DFFF.

#### 16.11.3.30 29 - Final Cartridge Plus

Size | 32Kb (1 bank of 32Kb)
EXROM | inactive (hi) (1)
GAME | inactive (hi) (1)
Load address | $0000-$7FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 1D 00 01 00 00 00 00 00 00  ???@????????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 80 10 00 00 00 00 00 00 80 00  CHIP??.???????.?
    0050: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF  ????????????????

This cart has 32Kb of ROM, bank 0 is in the cart image but is unused. The first 8Kb of the cart image is unused, the second 8Kb of the cart image is mapped to $E000-$FFFF, the third 8Kb of the cart image is mapped to $8000-$9FFF and the fourth 8Kb of the cart image is mapped to $A000-$BFFF. An NMI can be triggered by the cart, if address $0001 is written to and the cartridge is enabled. The cart can be disabled by software, by clearing bit 4 when writing to $DF00-$DFFF. Cart ROM at $E000-$FFFF can be disabled by setting bit 5 to 0 when writing to $DF00-$DFFF. Cart ROM at $8000-$BFFF can be disabled by setting bit 6 to 1 when writing to $DF00-$DFFF. Bit 7 of a byte written to $DF00-$DFFF can be read back from the cartridge if enabled (like a memory cell).

#### 16.11.3.31 30 - Action Replay 4

Size | 32Kb (4 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 1E 00 01 00 00 00 00 00 00  ???@????????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: EA 78 48 A9 7F 8D 0D DD D0 0E 48 AD 0D DD 10 04  .xP.??..?P?.??
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    2060: 09 80 0C 80 C3 C2 CD 38 30 4C E9 80 4C 81 81 4C  ?.?....80L?.LL
    ...
    4060: 43 48 49 50 00 00 20 10 00 00 00 02 80 00 20 00  CHIP????????.???
    4070: 09 80 0E 80 C3 C2 CD 38 30 A2 00 4C EF FC 20 BC  ?.?....80.?L?.??
    ...
    6070: 43 48 49 50 00 00 20 10 00 00 00 03 80 00 20 00  CHIP????????.???
    6080: 09 80 0C 80 C3 C2 CD 38 30 4C 70 88 4C 3F 80 4C  ?.?....80LpL?.L

The control register is the I/O-1 range:

        bit  meaning
        ---  -------
        0    Eprom banking bit 0 (bank address 13)
        1    Controls the GAME line (0 sets GAME low, 1 sets GAME high)
        2    Freeze-end bit (disables the register and hides any rom bank)
        3    Controls the Exrom line (1 sets EXROM low, 0 sets EXROM high)
        4    Eprom banking bit 1 (bank address 14)
        5-7  Unused

The first page of the currently banked ROM block can be read in the I/O-2 range.

#### 16.11.3.32 31 - Stardos

Size | 16Kb (2 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF (bank 0), $E000-$FFFF (bank 1)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 1F 00 01 00 00 00 00 00 00  ???@????????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: F9 80 B6 80 C3 C2 CD 38 30 FD 80 89 80 4C 0C 88  ?.¶....80...L?
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 00 E0 00 20 00  CHIP????????????
    2060: 85 56 20 0F BC A5 61 C9 88 90 03 20 D4 BA 20 CC  V???¥a.??.÷?.

This cart has 16Kb of ROM, of which the first 8Kb is mapped in at $8000-$9FFF and the second 8Kb is used as a kernel replacement. The kernel replacement is achieved by a clip that needs to be installed inside the C64.

Reading from I/O-1 causes a capacitor to get charged with every read, once the capacitor is charged enough it switches the cart on.

Reading from I/O-2 causes a different capacitor to get charged with every read, once the capacitor is charged enough it switched the cart off.

#### 16.11.3.33 32 - EasyFlash

Size | 1024Kb (64 banks of 2 * 8Kb)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $8000-$9FFF (ROML), $A000-$BFFF or $E000-$FFFF (ROMH)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 20 00 01 00 00 00 00 00 00  ???@????????????
    0020: 45 61 73 79 46 6C 61 73 68 20 43 61 72 74 72 69  EasyFlash?Cartri
    0030: 64 67 65 00 00 00 00 00 00 00 00 00 00 00 00 00  dge?????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    0050: 00 85 5E FE C3 C2 CD 38 30 93 0D 2B 2B 2B 20 45  ?^....80.?+++?E

EasyFlash is a 1 MByte Flash EPROM card with multiple configurations and banks possible, it also has 256 bytes of RAM which is mapped into the I/O-2 range.

There are two control registers, one at $DE00 and one at $DE02.

The register at $DE00 does the following:

        bit  meaning
        ---  -------
        7    LED control
        6-3  Unused
        2    Mode (0/1)
        1    Exrom line control
        0    Game line control

The register at $DE02 controls which bank is mapped into ROMH and ROML.

#### 16.11.3.34 33 - EasyFlash Xbank

Size | -
EXROM | -
GAME | -
Load address | -

This CRT type is not actually related to a seperate hardware, it is used by some EasyFlash related tools as a container format. Consequently VICE does (can) not load files of this type.

#### 16.11.3.35 34 - Capture

Size | 8Kb (1 bank of 8Kb)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $E000-$FFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 22 00 01 00 00 00 00 00 00  ???@???"????????
    0020: 4D 61 67 69 63 20 46 6F 72 6D 65 6C 00 00 00 00  Magic?Formel????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 01 E0 00 20 00  CHIP????????????
    0050: 00 0A 0D 8A B4 A1 20 80 00 0A 82 8A 8D 20 9E 20  ????.?.????

This cart has 8Kb of ROM which is mapped to $E000, and 8Kb of RAM which is mapped to $6000. The cartridge is disabled after a reset.

When the freeze button is pressed the following happens:

- an NMI is generated
- as soon as the current adress is in bank 0xfe the cart switches to ultimax mode. The cart ROM then contains one page full of "jmp $eaea", which ultimately calls the freezer code.
- the $FFF7/$FFF8 "register" logic is enabled and any access (read or write) to $FFF7 will turn the cart_enabled off (leave ultimax mode), and an access to $FFF8 will turn the cart back on (enter ultimax mode). the "register logic" that causes this can only be disabled again by a hardware reset.

#### 16.11.3.36 35 - Action Replay 3

Size | 16Kb (2 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 23 00 01 00 00 00 00 00 00  ???@???#????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: EA A9 E3 48 A9 7B 48 08 4C 1A 80 EA EA EA 48 AD  ...H..H?L?....H
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    2060: 09 80 5E FE C3 C2 CD 38 30 78 A2 FB D8 9A A9 27  ?.^....80x.....'

This cart has 16Kb of ROM of which 8Kb is mapped in at both ROML and ROMH. Bank switching and control register is done through the I/O-1 range:

        bit  meaning
        ---  -------
        7-4  unused
        3    Exrom line control
        2    Disable cart
        1    Unused
        0    Bank

#### 16.11.3.37 36 - Retro Replay

Size | 32Kb, 64Kb or 128Kb (4, 8 or 16 banks of 8Kb)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 24 00 00 00 00 00 00 00 00  ???@???$????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 09 80 0C 80 C3 C2 CD 38 30 4C 7F 81 4C 87 81 4C  ?.?....80L?L.L

The Retro Replay has three registers: Two write-only ($DE00 & $DE01) and one read-only register ($DE00 & $DE01 giving the same results).

The register at $DE00 is reset to $00 on a hard reset if not in flash mode. If in flash mode, it is set to $02 in order to prevent the computer from starting the normal cartridge. Flash mode is selected with a jumper.

Register at $DE00:

        bit  meaning
        ---  -------
        0    Controls the GAME line: A 1 asserts the line, a 0  will  deassert
             it.
        1    Controls the EXROM line: A 0 will assert it, a  1  will  deassert
             it.
        2    Writing a 1 will disable further write accesses to all  registers
             of the Retro Replay, and  set  the  memory  map  of  the  C64  to
             standard, as if there is no cartridge installed at all.
        3    Controls bank-address 13 for ROM and RAM banking.
        4    Controls bank-address 14 for ROM and RAM banking.
        5    Switches between ROM and RAM: 0=ROM, 1=RAM
        6    Must be written once to "1" after a successful freeze in order to
             set the correct memory map and  enable  bits  0  and  1  of  this
             register. Otherwise no effect.
        7    Controls bank-address 15 for ROM banking.

The register at $DE01 is the extended control register. If not in Flash mode, bits 1, 2 and 6 can only be written once. If in Flash mode, the REUcomp bit cannot be set, but the register will not be disabled by the first write. Bit 5 is always set to 0 if not in Flash mode.

Register at $DE01:

        bit  meaning
        ---  -------
        0    Enable clockport connector.
        1    AllowBank (1 allows banking of RAM in $DF00/$DE02 area)
        2    NoFreeze (1 disables Freeze function)
        3    Bank-address 13 for RAM and ROM (mirror of $DE00)
        4    Bank-address 14 for RAM and ROM (mirror of $DE00)
        5    Bank-address 16 for ROM (only in flash mode)
        6    REU compatibility bit. 0=standard memory map, 1 = REU  compatible
             memory map
        7    Bank-address 15 for ROM (mirror of $DE00)

Reading from the registers at either $DE00 or $DE01 will return the content of the status register.

Status register:

        bit  meaning
        ---  -------
        0    1=Flashmode active (jumper set)
        1    feedback of AllowBank bit
        2    1=Freeze button pressed
        3    feedback of banking bit 13
        4    feedback of banking bit 14
        5    feedback of banking bit 16
        6    1=REU compatible memory map active
        7    feedback of banking bit 15

The following memory maps are available:

- standard - $DE00 and $DE01 registers are active, $DF00-$DFFF contain the last page of the selected 8Kb bank of either ROM or RAM, whatever is selected. RAM can only be accessed in $8000-$9FFF. ROM can be mapped to $8000, $A000 or $E000 with the corresponding status on GAME and EXROM. Note: If the AllowBank bit is not set, the $DF00-$DFFF area will always access bank 0 of the RAM, so the older cartridge images will work. The AllowBank bit does not have any effect on the ROM mirror in that area.
- Freeze - ROM is mapped to $E000-$FFFF, bank 0 is active directly after Freeze. Writing to bits 0 and 1 of the $DE00 register will have no effect on GAME and EXROM. RAM can be selected and used in $DF00 or $DE02, respectively, but not in $8000. Banking bits work, so you have full read access to the ROM, and access to up to four RAM pages with the AllowBank bit set (minus 2 bytes if REU compatible bit is set). You should leave this memory map ASAP by setting bit 6 of $DE00, because C64 RAM in the $E000 area is not available, and you don't have control of the GAME and EXROM lines.
- REU compatible - $DE00 and $DE01 registers are active, $DE02-$DEFF contain a mirror of $9E02-$9EFF of the selected 8K-bank of either ROM or RAM, whatever is selected. RAM can only be accessed in $8000-$9FFF. ROM can be mapped to $8000, $A000 or $E000 with the corresponding status on GAME and EXROM. The $DF00 stays free for use with the 1764 Ram Expansion Unit (REU). Note: If the AllowBank bit is not set, the $DE02-$DEFF area will always access bank 0 of the RAM, so the older cartridge images will work. The AllowBank bit does not have any effect on the ROM mirror in that area.

#### 16.11.3.38 37 - MMC64

Size | 8Kb (1 bank of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 25 00 01 00 00 00 00 00 00  ???@???%????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 09 80 64 97 C3 C2 CD 38 30 78 D8 A2 FF 9A 20 D4  ?.d...80x..?.?.

The clockport registers of this cart can be switched to either $DE01-$DE0F or $DF21-$DF2F. The control registers are available at $DF10-$DF13.

The register at $DE01 / $DF21 is write only:

        bit  meaning
        ---  -------
        7-1  Unused
        0    0 = disable clock port, 1 = enable clockport

The registers at $DE02-$DE0F / $DF22-$DF2F are for the clock port and are read/write.

The register at $DF10 is the MMC64 SPI transfer register, a byte written to this registers is sent to the card & response from the card is read here.

The register at $DF11 is the MMC64 control register:

        bit  meaning
        ---  -------
        0    0 = MMC64 BIOS active, 1 = external ROM active
        1    0 = card selected, 1 = card not selected
        2    0 = 250khz transfer, 1 = 8mhz transfer
        3    0 = clock port @ $DE00, 1 = clock port @ $DF20
        4    0 = normal Operation, 1 = flash mode (*)
        5    0 = allow external rom when BIOS is disabled,
             1 = disable external ROM
        6    0 = SPI write trigger mode, 1 = SPI read trigger mode
        7    0 = MMC64 is active, 1 = MMC64 is completely disabled (**)

(*) bit can only be programmed when flash jumper is set (**) bit can only be modified after unlocking

The register at $DF12 is the MMC64 status register, which is read-only:

        bit  meaning
        ---  -------
        0    0 = SPI ready, 1 = SPI busy
        1    external GAME line
        2    external EXROM line
        3    0 = card inserted, 1 = no card inserted
        4    0 = card write enabled, 1 = card write disabled
        5    0 = flash jumper not set, 1 = flash jumper set
        6-7  unused

The register at $DF13 is the MMC64 identification register, which when reading from it can have the following values:

$64 when bit 1 of $DF11 is 0. $01 when bit 1 of $DF11 is 1 and REV A hardware is used. $02 when bit 1 of $DF11 is 1 and REV B hardware is used.

when writing to it it can be used to unlock bit 7 of $DF11 or to re-enable the cart:

Write $55 & $AA into this register to unlock bit 7 of $DF11. Write $0A & $1C into this register to re-enable MMC64 hardware.

#### 16.11.3.39 38 - MMC Replay

Size | 64Kb or 512Kb (8 or 64 banks of 8Kb)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 26 00 00 00 00 00 00 00 00  ???@???&????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 1A 80 6E 9E C3 C2 CD 38 30 4D 4D 43 52 45 50 4C  ?.n...80MMCREPL

The cart uses the following registers:

$DE00 - RR control register write

        bit  meaning
        ---  -------
        0    GAME line
        1    EXROM line
        2    1 = disable RR, bit can be reset by setting bit 6 of $DF12
        3    bank address 13
        4    bank address 14
        5    0 = rom enable, 1 = ram enable
        6    1 = exit freeze mode
        7    bank address 15

$DE01 - extended RR control register write

        bit  meaning
        ---  -------
        0    0 = disable clockport, 1 = enable clockport
        1    0 = disable I/O RAM banking, 1 = enable I/O RAM banking
        2    0 = enable freeze, 1 = disable freeze
        3    bank address 13 (mirror of $DE00)
        4    bank address 14 (mirror of $DE00)
        5    0 = enable MMC registers, 1 = disable MMC registers. Can only  be
             written when bit 6 of $DF12 is 1. Register becomes effective when
             bit 0 of $DF11 is 1.
        6    0 = RAM/ROM at $DFxx, 1 = RAM/ROM at $DExx
        7    bank address 15 (mirror of $DE00)

$DE02-$DE0F - Clockport memory area (when enabled)

$DF10 - MMC SPI transfer register, a byte written is sent to the card & response from the card is read here.

$DF11 - MMC control register

        bit  meaning
        ---  -------
        0    0 = MMC BIOS enabled, 1 = MMC BIOS disabled.  Enabling  MMC  BIOS
             sets ROM banking to the last 64Kb bank.
        1    0 = card selected, 1 = card not selected. This bit also  controls
             the green activity LED.
        2    0 = 250khz transfer, 1 = 8mhz transfer
        3    ALWAYS 0
        4    ALWAYS 0
        5    (in RR-Mode:)
              0 = allow RR rom when MMC BIOS disabled , 1 = disable RR ROM
              (in mmcreplay bios mode:)
              RAM banking (0 = $E000 - $FFFF, 1 = $8000 - $9FFF)
              (in 16K mode:)
              enable RAM at $A000 - $BFFF
        6    0 = SPI write trigger mode, 1 = SPI read trigger mode
        7    ALWAYS 0

$DF12 - MMC status register

        bit  meaning
        ---  -------
        0    0 = SPI ready, 1 = SPI busy (read)
                            1 = forbid ROM  write  accesses  (write).  Setting
                            this bit will disable writes  to  ROM  until  next
                            reset
        1  feedback of $DE00 bit 0 (GAME)
        2  feedback of $DE00 bit 1 (EXROM)
        3  0 = card inserted, 1 = no card inserted
        4  0 = card write enabled, 1 = card write disabled
        5  EEPROM DATA line /  DDR  register.  Setting  DATA  to  "1"  enables
           reading data bit from EEPROM at this position.
        6  0 = RR compatibility mode, 1 = Extended mode
           Selecting RR compatibility mode limits RAM  to  32Kb  and  disables
           writes  to  extended  banking  register.  Selecting  Extended  mode
           enables full RAM banking and enables Nordic Power mode in RR mode.
        7  EEPROM CLK line

$DF13 - Extended banking register Can only be read/written to when bit 6 of $DF12 is 1

        bit  meaning
        ---  -------
        0    bank address 16
        1    bank address 17
        2    bank address 18
        3    ALWAYS 0
        4    ALWAYS 0
        5    16K rom mapping
        6    1 = enable  RR  register.  Disabling  RR  register  disables  ALL
             ROM/RAM banking too.
        7    ALWAYS 0

#### 16.11.3.40 39 - IDE64

Size | 64Kb or 128Kb (4 or 8 banks of 16Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 27 00 01 00 00 00 00 00 00  ???@???'????????
    0020: 49 44 45 36 34 20 43 41 52 54 52 49 44 47 45 20  IDE64 CARTRIDGE?
    0030: 49 44 45 44 4f 53 20 32 30 31 33 31 32 31 32 00  IDEDOS 20131212?
    0040: 43 48 49 50 00 00 40 10 00 02 00 00 80 00 40 00  CHIP????????.???
    0050: 63 80 5E FE C3 C2 CD 38 30 20 49 44 45 36 34 20  c.^....80?IDE64?

The IDE64 cart uses the following registers:

        $DE20 - $DE2F IDE BUS Registers
        $DE30 - Low Data HDD register
        $DE31 - High Data HDD register

$DE32 register:

        bit  meaning
        ---  -------
        7    unused (0)
        6    unused (0)
        5    unused (0)
        4    version number (1)
        3    romaddr15
        2    romaddr14
        1    game
        0    exrom

        $DE32 - $DE35 = IDE64 ROM bank select registers
        $DE5F         = RTC access (bit 0 only to serial accessed RTC)
        $DE60 - $DEFF = ROM used by software
        $DEFB         = IDE64 clock reset, kill the cartridge
        $DEFC - $DEFF = IDE64 memory configuration registers

#### 16.11.3.41 40 - Super Snapshot V4

Size | 32Kb (4 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 28 00 01 00 00 00 00 00 00  ???@???(????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 80 AD B5 80 C3 C2 CD 38 30 08 48 A9 06 8D 00 DF  .µ....80?P.???
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 00 A0 00 20 00  CHIP???????? ???
    2060: 4C FA A0 A9 07 8D 00 DD 2C 00 DD 50 FB 2C 00 DD  L? .??.,?.P.,?.
    ...
    4060: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    4070: 13 80 BC FE C3 C2 CD 38 30 08 48 A9 02 8D 00 DF  ?.?....80?H.???
    ...
    6070: 43 48 49 50 00 00 20 10 00 00 00 01 A0 00 20 00  CHIP???????? ???
    6080: F0 8A 48 A9 00 85 22 85 23 8D 53 0F 20 0C A1 B0  ?H.?"#S???.°

This cart has 32Kb of ROM and 8Kb of RAM, it uses I/O-1 as a mirror of the last page of cart RAM. It has the following registers in the I/O-2 range:

ROM config register at $DF00 (can only be written to):

        bit  meaning
        ---  -------
        0    ?
        1    ? (write 1 to release freeze mode)
        2    ROM bank select
        3    write 1 to disable cartridge
        4-6  unused
        7    ?

Note: if bit0, bit1, bit7 are all 0, then ultimax mapping is selected and RAM is enabled at ROML, otherwise if bit 0 is 0, then 16Kb mapping is enabled, or if bit 0 is 1, then 8Kb mapping is enabled.

RAM config register at $DF01 (read/write):

If written value == last value - 1, then ultimax mapping is selected and RAM is enabled at ROML, if written value == last value + 1, then ROM is enabled at ROML and exrom is deasserted (switch to either 8k or 16k mapping)

$DF02-$DFFF holds the last page of the first 8kb of the current bank.

#### 16.11.3.42 41 - IEEE-488

Size | 4Kb (1 bank of 4Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$8FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 29 00 01 00 00 00 00 00 00  ???@???)????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 10 10 00 00 00 00 80 00 10 00  CHIP????????.???
    0050: 09 80 7A 80 C3 C2 CD 38 30 8E 16 D0 20 84 FF 20  ?.z....80?.???

The cart uses a TPI for the IEEE488 interface/communication in the I/O-2 range:

        $DF00 - Port A Data
        $DF01 - Port B Data
        $DF02 - Port C Data
        $DF03 - Port A Direction
        $DF04 - Port B Direction
        $DF05 - Port C Direction
        $DF06 - Control register
        $DF07 - Active Interrupt register

#### 16.11.3.43 42 - Game Killer

Size | 8Kb (1 bank of 8Kb)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $E000-$FFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 2A 00 00 00 00 00 00 00 00  ???@???*????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 E0 00 20 00  CHIP????????????
    0050: 00 25 08 CF 07 9E 32 30 38 38 20 4D 43 2E 43 52  ?%?.?2088?MC.CR

When the cartridge is active, ultimax is enabled when the address being accessed is is the $E000-$FFFF range, so the ROM is visible at $E000, below is normal C64 RAM. The cart can be disabled by writing to either I/O-1 or I/O-2 range. When the freezer button is pressed, the cartridge will be enabled and an NMI will be triggered.

#### 16.11.3.44 43 - Prophet64

Size | 256Kb (32 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 2B 00 01 00 00 00 00 00 00  ???@???+????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 09 80 09 80 C3 C2 CD 38 30 78 A0 00 84 F8 84 FA  ?.?....80x ???

The control register is the I/O-2 range:

        bit  meaning
        ---  -------
        7-6  unused
        5    disable cart
        4-0  bank select

#### 16.11.3.45 44 - EXOS

Size | 8Kb (1 bank of 8Kb)
EXROM | inactive (hi) (1)
GAME | active (lo) (0)
Load address | $E000-$FFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 2C 01 00 00 00 00 00 00 00  ???@???,????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 E0 00 20 00  CHIP????????????
    0050: 85 56 20 0F BC A5 61 C9 88 90 03 20 D4 BA 20 CC  V???¥a.??.÷?.

This cart has 8Kb of ROM, mapped in at $E000-$FFFF only when hirom is selected. The cart uses a clip that needs to be installed inside the C64.

#### 16.11.3.46 45 - Freeze Frame

Size | 8Kb (1 bank of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 2D 00 01 00 00 00 00 00 00  ???@???-????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 10 80 10 80 C3 C2 CD 38 30 20 00 00 00 00 00 00  ?.?....80???????

When reading from the I/O-1 range the cart is enabled, when reading from the I/O-2 range the cart is disabled. When the freeze button is pressed the ROM is mapped to both $8000-$9FFF and $E000-$FFFF.

#### 16.11.3.47 46 - Freeze Machine

Size | 16Kb or 32Kb (2 or 4 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 2E 00 01 00 00 00 00 00 00  ???@???.????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 3A 83 60 80 C3 C2 CD 38 30 20 00 00 40 00 00 00  :`....80???@???
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 00 A0 00 20 00  CHIP???????? ???
    2060: 78 A9 34 85 01 A0 00 B1 F8 91 F6 E6 F8 D0 02 E6  x.4? ?±?.?µ?.?µ
    ...
    4060: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    4070: 3A 83 60 80 C3 C2 CD 38 30 20 00 00 40 00 00 00  :`....80???@???
    ...
    6070: 43 48 49 50 00 00 20 10 00 00 00 01 A0 00 20 00  CHIP???????? ???
    6080: 78 A9 34 85 01 A0 00 B1 F8 91 F6 E6 F8 D0 02 E6  x.4? ?±?.?µ?.?µ

Warning, the following information is based on guess-work and might be incorrect, any further information and/or corrections are appreciated.

When reading from the I/O-1 range ROM bank 0(/2) is mapped to $8000-$9FFF and ROM bank 1(/3) is mapped to $A000-$BFFF. When reading from the I/O-2 range the cart is disabled. When a reset happens the ROM banks get switched and ROM bank 0(/2) is mapped to $8000-$9FFF. When a freeze happens ROM bank 0(/2) is mapped to both $8000-$9FFF and $E000-$FFFF.

#### 16.11.3.48 47 - Snapshot 64

Size | 4Kb (1 bank of 4Kb)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $E000-$EFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 2F 00 00 00 00 00 00 00 00  ???@???/????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 10 10 00 00 00 00 E0 00 10 00  CHIP????????????
    0050: 78 D8 48 8A 48 98 48 AC 0D DD 10 03 4C EE F2 AD  x.HHH??.??L??

Warning, the following information is based on guess-work and might be incorrect, any further information and/or corrections are appreciated.

The cart has a control bit (bit 0) in the I/O-2 range which is used to disable or enable the cart.

#### 16.11.3.49 48 - Super Explode V5.0

Size | 16Kb (2 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 30 00 01 00 00 00 00 00 00  ???@???0????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: D7 86 5E FE C3 C2 CD 38 30 A9 00 2C A9 FF 85 FE  .^....80.?,.?.
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    2060: E8 96 5E FE C3 C2 CD 38 30 20 6C 81 A9 09 8D 99  ?^....80?l.?

Warning, the following information is based on guess-work and might be incorrect, any further information and/or corrections are appreciated.

The cart has 16Kb of ROM which are used as two banks of 8Kb, they are mapped into $8000-$9FFF and the last page of the current ROM bank is mirrored in $DF00-$DFFF. The cart has a control bit (bit 7) at $DF00, which is used to select what ROM bank is used.

#### 16.11.3.50 49 - Magic Voice

Size | 16Kb (2 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Load address | $8000-$9FFF (bank 1), $A000-$BFFF (bank 2)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 31 00 01 00 00 00 00 00 00  ???@???1????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: EA 2C 80 DF 50 FB A0 00 8C 80 DF B9 E3 A3 29 0F  .,.?P. ?.?¹.£)?
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 00 A0 00 20 00  CHIP???????? ???
    2060: 4A EB C0 49 6A EA BB FB 4E CA 43 1E 75 63 15 97  J?.Ij.».N.C?uc?

This cart has 16Kb of ROM, mapped in at reset at $8000-$BFFF. The cart is controled through a TPI at $DF80-$DF87:

        $DF80 - Port A Data
        $DF81 - Port B Data
        $DF82 - Port C Data
        $DF83 - Port A Direction
        $DF84 - Port B Direction
        $DF85 - Port C Direction
        $DF86 - Control register
        $DF87 - Active Interrupt register

The cart has a pass-through port and does the following at start-up:

- Program starts after reset at $FFD3, and copies code from $FF36-$FFD2 to $0200-$029C (157 bytes)
- Program continues at $021A, copies $A000-$BFFF from EPROM to RAM at $A000-$BFFF (8Kb), copies $E000-$FFFF from EPROM to RAM at $E000-$FFFF (8Kb), copies $AE62-$B461 from RAM to RAM at $C000-$C5FF (Magic Voice Code)
- Jump to beginning of Magic Voice code at $C000

#### 16.11.3.51 50 - Action Replay 2

Size | 16Kb (2 banks of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Startup mode | 8k Game
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 32 00 01 00 00 00 00 00 00  ???@???2????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: EA EA 68 AA 68 85 94 68 85 95 68 85 96 68 85 97  ..h×hhhh
    ...
    2050: 43 48 49 50 00 00 20 10 00 00 00 01 80 00 20 00  CHIP????????.???
    2060: 30 80 5E FE C3 C2 CD 38 30 20 04 90 4C 38 DF 1A  0.^....80??L8??

Warning, the following information is based on guess-work and might be incorrect, any further information and/or corrections are appreciated.

I/O-1 is somehow used to enable the cart, the exact way in which this is done is unknown. Reading from the I/O-2 range will give you the last page of the current ROM bank, and writing to it will disable the cart.

#### 16.11.3.52 51 - MACH 5

Size | 4Kb or 8Kb (1 bank of 4Kb or 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Startup mode | 8k Game
Load address | $8000-$8FFF (4Kb), $8000-$9FFF (8Kb)

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 33 00 01 00 00 00 00 00 00  ???@???3????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: AF 83 5E FE C3 C2 CD 38 30 4D 41 43 48 35 A5 93  »^....80MACH5¥.

This cart has 8Kb ROM mapped at $8000-$9FFF, the $9E00-$9EFF range is mirrored at $DE00-$DEFF and the $9F00-$9FFF range is mirrored at $DF00-$DFFF.

#### 16.11.3.53 52 - Diashow maker

Size | 8Kb (1 bank of 8Kb)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Startup mode | 8k Game
Load address | $8000-$9FFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 34 00 01 00 00 00 00 00 00  ???@???4????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 20 10 00 00 00 00 80 00 20 00  CHIP????????.???
    0050: 09 80 09 80 C3 C2 CD 38 30 AD 11 D0 29 10 D0 62  ?.?....80?.)?.b

Accessing I/O-1 (the software uses $DE00 only it seems) disables cartridge ROM. A reset enables 8K game mode and the ROM bank is mapped to $8000. A freeze causes ROM to be mapped to $8000.

#### 16.11.3.54 53 - Pagefox

Size | 64Kb (4 banks of 16Kb)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Startup mode | 16k Game
Load address | $8000-$BFFF

          00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
          -----------------------------------------------  ----------------
    0000: 43 36 34 20 43 41 52 54 52 49 44 47 45 20 20 20  C64?CARTRIDGE???
    0010: 00 00 00 40 01 00 00 35 01 01 00 00 00 00 00 00  ???@???5????????
    0020: 56 49 43 45 20 43 41 52 54 00 00 00 00 00 00 00  VICE?CART???????
    0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????
    0040: 43 48 49 50 00 00 40 10 00 00 00 00 80 00 40 00  CHIP??@?????.?@?
    0050: 31 80 BB 0E C3 C2 CD 38 30 50 46 20 56 31 2E 30  1.»?...80PF?V1.0
    ...
    4050: 43 48 49 50 00 00 40 10 00 00 00 01 80 00 40 00  CHIP??@?????.?@?
    4060: A2 FE 9A 20 EC AE 20 82 80 20 74 86 20 A5 8B 4C  ...??®?.?t?¥L
    ...
    8060: 43 48 49 50 00 00 40 10 00 00 00 02 80 00 40 00  CHIP??@?????.?@?
    8070: 5A 01 02 03 04 06 0A 0B 10 14 1E 28 3C 00 00 00  Z??????????(<???
    ...
    C070: 43 48 49 50 00 00 40 10 00 00 00 03 80 00 40 00  CHIP??@?????.?@?
    C080: 1E 03 14 82 09 05 09 0F 0C 0D 0F 05 09 09 0B 0A  ???????????????

This cart has 64Kb ROM (2 32Kb Eproms, mapped to $8000 and $A000 in 16Kb Game Mode), and 32Kb RAM (mapped to $8000 and $A000 in 16K Game Mode). The cart has 1 (write-only) bank control register which is located at $DE80 and mirrored throughout the $DE80-$DEFF range:

        Bit 0: unused/don't care
        Bit 1: Bank select: 0=upper, 1=lower (not correct ?!)
        Bit 2: chip select 0
        Bit 3: chip select 1
        Bit 4: cartridge enable/disable: 0=enable, 1=disable
        Bits 5-7: unused/don't care

Chip select combinations of 0/1 are:

        00: Eprom "79"
        01: Eprom "ZS3"
        10: Ram
        11: empty space (reading returns VIC-II data)

note: on the original hardware "disabling" the cartridge by setting bit 4 of the control register does NOT prevent write accesses to the cartridge RAM!. So to actually disable the RAM, it is suggested to write $FF to the register.

#### 16.11.3.55 54 - Kingsoft

Size | -
EXROM | active (lo) (0)
GAME | active (lo) (0)
Startup mode | 16k Game
Load address | -

#### 16.11.3.56 55 - Silverrock 128

Size | 128k (16 banks of 8k)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Startup mode | 8k Game
Load address | $8000-$9FFF

#### 16.11.3.57 56 - Formel 64

Size | 32kb (4 banks of 8k)
EXROM | active (lo) (0)
GAME | active (lo) (0)
Load address | $E000-$FFFF

#### 16.11.3.58 57 - RGCD

Size | 64kb (8 banks of 8k)
EXROM | active (lo) (0)
GAME | inactive (hi) (1)
Startup mode | 8k Game
Load address | $8000-$9FFF

This cartridge type is very similar to the Magic Desk cart type: ROM memory is organized in 8Kb ($2000) banks located at $8000-$9FFF. Bank switching is done by writing the bank number to $DE00.

        bit 0-2   bank number
        bit 3     exrom (1 = cart disabled)

## 16.12 The PSID image format for ripped SID tunes

This section describes the SID file format used for SID tunes in the HVSC (High Voltage SID Collection - http://hvsc.de). It is based mostly on Michael Schwendt's document that describes the file format and the PSID v2NG extensions described by Simon White and Dag Lem and was further extended by Wilfred Bos (PSID v3, RSID v3) and LaLa (assembled most of the following text) and last not least tweaked a bit by Groepaz to fit into the VICE documentation.

SID files use the .sid file extension.

Since PSID v2 is simply an extension of PSID v1, PSID v2NG is an extension of PSID v2, RSID is a restricted version of PSID v2NG, PSID v3 and RSID v3 are extentions of PSID v2NG and RSID v2, all of the formats are discussed together below. RSID in specific is discussed in detail under the 'magicID' field description.

The information presented here targets programmers or other people with reasonable background. It is not suitable for newbies who have never before used a machine code monitor, a disassembler, or a hexadecimal editor.

### 16.12.1 The SID file header v1

The detailed structure of the SID header looks like the following. Header offsets are in hexadecimal notation. Other integer values are decimal unless explicitly marked otherwise. Any stored integer values are in big-endian format:

    +00    magicID: ``PSID'' or ``RSID''

This is a four byte long ASCII character string containing the value 0x50534944 or 0x52534944. 'RSID' (Real SID) denotes that the file strictly requires a true Commodore-64 environment to run properly. 'PSID' files will generally run trouble-free on older PlaySID and libsidplay1 based emulators, too.

Some words about the Real C64 SID file format (RSID):

The RSID format was designed to contain tunes that are not PlaySID compatible, but strictly require a real C64 environment to run. Tunes that are multi-speed and/or contain samples and/or use additional interrupt sources or do busy looping will cause older SID emulators to lock up or play very wrongly (if at all).

By using the name RSID for such rips all existing SID emulators will reject these tunes safely until they can be upgraded to cope with the additional requirements.

Due to the nature of these tunes, every effort must be made to make sure they are directly runnable on an actual C64 computer. As such the tunes will only be presented with the default C64 power-on environment and expected to configure and use all hardware appropriately.

RSID is based on PSIDv2NG with the following modifications:

- magicID = RSID
- version = 2 and 3 only
- loadAddress = 0 (reserved)
- playAddress = 0 (reserved)
- speed = 0 (reserved)
- psidSpecific flag is called C64BASIC flag

The above fields MUST be checked and if any differ from the above then the tune MUST be rejected. The definitions above will force tunes to contain proper hardware configuration code and install valid interrupt handlers.

The default C64 environment is as follows:

- VIC - IRQ set to raster $137, but not enabled.
- CIA 1 timer A - set to 60Hz with the counter running and IRQs active.
- Other timers - disabled and loaded with $FFFF.
- Bank register - $37

A side effect of the bank register is that init MUST NOT be located under a ROM/IO memory area (addresses $A000-$BFFF and $D000-$FFFF) or outside the load image. Since every effort needs to be made to run the tune on a real C64 the load address of the image MUST NOT be set lower than $07E8.

    +04    WORD version

Available version number can be 0001, 0002 or 0003. Headers of version 2 and 3 provide additional fields. RSID and PSID v2NG files must have 0002 or 0003 here.

    +06    WORD dataOffset

This is the offset from the start of the file to the C64 binary data area. Because of the fixed size of the header, this is either 0x0076 for version 1 and 0x007C for version 2 and 3.

    +08    WORD loadAddress

The C64 memory location where to put the C64 data. 0 means the data are in original C64 binary file format, i.e. the first two bytes of the data contain the little-endian load address (low byte, high byte). This must always be true for RSID files. Furthermore, the actual load address must NOT be less than $07E8 in RSID files.

You must be absolutely sure what to enter here. There is no way to detect automatically whether the first two bytes in a C64 data file are meant to be a load address or some arbitrary bytes of code or data. Unless your C64 file is not a normal binary file and thus has no load address in front, you need not enter anything else than 0 here. The SID tune will not play if you specify a load address which is present in the C64 file already.

Normal C64 binary data files have a load address in their first two bytes, so they can be loaded to a pre-defined destination address by executing LOAD"FILE",8,1, for instance. If a load address is explicitly specified in the sidtune info file, some sidtune converters and utilities conjecture that the C64 data don't have a load address in their first two bytes. Hence, the explicit load address from the info file is moved in front of the C64 data to create a valid C64 binary file which can be easily loaded on a C64, too. If that C64 file were to be saved, it would contain two superfluous data bytes at offset 2 if an original load address had been in the first two bytes of the old file. This process of adding a duplicate load address can be repeated. The file loader strips off the first two bytes (the used load address) and puts the rest of the file contents (including the now obsolete load address at file offset 2) into memory. If the new load address is the same than the old one the two added bytes cause the whole data to be displaced by two bytes, which most likely results in malfunctioning code. Also, superfluous bytes in memory then can confuse disassemblers which start at the beginning of the file or memory buffer.

    +0A    WORD initAddress

The start address of the machine code subroutine that initializes a song, accepting the contents of the 8-bit 6510 Accumulator as the song number parameter. 0 means the address is equal to the effective load address.

In RSID files initAddress must never point to a ROM area ($A000-$BFFF or $D000-$FFFF) or be lower than $07E8. Also, if the C64 BASIC flag is set, initAddress must be 0.

    +0C    WORD playAddress

The start address of the machine code subroutine that can be called frequently to produce a continuous sound. 0 means the initialization subroutine is expected to install an interrupt handler, which then calls the music player at some place. This must always be true for RSID files.

    +0E    WORD songs

The number of songs (or sound effects) that can be initialized by calling the init address. The minimum is 1. The maximum is 256.

    +10    WORD startSong

The song number to be played by default. This value is optional. It often specifies the first song you would hear upon starting the program is has been taken from. It has a default of 1.

    +12    LONGWORD speed

This is a 32 bit big endian number.

For version 1 and 2 and for version 2NG and 3 with PlaySID specific flag (+76) set, the 'speed' should be handled as follows:

Each bit in 'speed' specifies the speed for the corresponding tune number, i.e. bit 0 specifies the speed for tune 1. If there are more than 32 tunes, the speed specified for tune 32 is the same as tune 1, for tune 33 it is the same as tune 2, etc.

For version 2NG and 3 with PlaySID specific flag (+76) cleared, the 'speed' should be handled as follows:

Each bit in 'speed' specifies the speed for the corresponding tune number, i.e. bit 0 specifies the speed for tune 1. If there are more than 32 tunes, the speed specified for tune 32 is also used for all higher numbered tunes.

For all version counts:

- A 0 bit specifies vertical blank interrupt (50Hz PAL, 60Hz NTSC), and a 1 bit specifies CIA 1 timer interrupt (default 60Hz).
- Surplus bits in 'speed' should be set to 0.
- For RSID files 'speed' must always be set to 0.

Note that if 'play' = 0, the bits in 'speed' should still be set for backwards compatibility with older SID players. New SID players running in a C64 environment will ignore the speed bits in this case.

WARNING: This field does not work in PlaySID for Amiga like it was intended, therefore the above is a redefinition of the original 'speed' field in SID v2NG! See also the 'clock' (video standard) field described below for 'flags'.

    +16    ``<name>''
    +36    ``<author>''
    +56    ``<released>'' (once known as ``<copyright>'')

These are 32 byte long ASCII character strings. Upon evaluating the header, these fields may hold a character string of 32 bytes which is not zero terminated. For less than 32 characters the string should be zero terminated. The maximum number of available free characters is 32.

    +76    <data>

Version 1 of the SID header is complete at this point. The binary C64 data starts here.

### 16.12.2 The SID file header v2 and v3

Version 2 and 3 of the header incorporates the v1 header fields and provides additional fields. Some of these are actually v2NG or v3 specific - those are noted below.

    +76    WORD flags

This is a 16 bit big endian number containing the following bitfields:

- Bit 0 specifies format of the binary data (musPlayer): 0 = built-in music player, 1 = Compute!'s Sidplayer MUS data, music player must be merged.

If this bit is set, the appended binary data are in Compute!'s Sidplayer MUS format, and does not contain a built-in music player. An external player machine code must be merged to replay such a sidtune.

- Bit 1 specifies whether the tune is PlaySID specific, e.g. uses PlaySID samples (psidSpecific): 0 = C64 compatible, 1 = PlaySID specific (PSID v2NG, v3) 1 = C64 BASIC flag (RSID)

This is a v2NG and RSID specific field.

PlaySID samples were invented to facilitate playback of C64 volume register samples with the original Amiga PlaySID software. PlaySID samples made samples a reality on slow Amiga hardware with a player that was updated only once a frame.

Unfortunately, converting C64 volume samples to PlaySID samples means that they can no longer be played on a C64, and furthermore the conversion might potentially break the non-sample part of a tune if the timing between writes to the SID registers is at all altered. This follows from the ADSR bugs in the SID chip.

Today, the speed of common hardware and the sophistication of the SID players is such that there is little need for PlaySID samples. However, with all the PlaySID sample PSIDs in existence there's a need to differentiate between SID files containing only original C64 code and PSID files containing PlaySID samples or having other PlaySID specific issues. As stated above, bit 1 in 'flags' is reserved for this purpose.

Since RSID files do not have the need for PlaySID samples, this flag is used for a different purpose: tunes that include a BASIC executable portion will be played (with the BASIC portion executed) if the C64 BASIC flag is set. At the same time, initAddress must be 0.

- Bits 2-3 specify the video standard (clock): 00 = Unknown, 01 = PAL, 10 = NTSC, 11 = PAL and NTSC.

This is a v2NG specific field.

As can be seen from the 'speed' field, it is not possible to specify NTSC C64 playback. This is unfortunate, since the different clock speeds means that a tune written for the NTSC C64 will be slightly detuned if played back on a PAL C64. Furthermore, NTSC C64 tunes driven by a vertical blank interrupt have to be converted to use the CIA 1 timer to fit into this scheme. This can cause severe problems, as the NTSC refresh rate is once every 17045 cycles, while the CIA 1 timer A is latched with 17095 cycles. Apart from the difference in timing itself, the SID ADSR bugs can actually break the tune.

The 'clock' (video standard) field was introduced to circumvent this problem.

- Bits 4-5 specify the SID version (sidModel): 00 = Unknown, 01 = MOS6581, 10 = MOS8580, 11 = MOS6581 and MOS8580.

This is a v2NG specific field.

- Bits 6-7 specify the SID version (sidModel) of the second SID: 00 = Unknown, 01 = MOS6581, 10 = MOS8580, 11 = MOS6581 and MOS8580.

This is a v3 specific field.

The MOS6581 and the MOS8580 have three notable differences. First, combined waveforms are generally louder on a MOS8580, to the extent that some combinations that are clearly audible on a MOS8580 are completely silent on a MOS6581. Second, the internal DC levels in the MOS8580 are so small that software or hardware tricks must be used to play volume samples. Third, the MOS8580 analog filter has totally different characteristics from the MOS6581 analog filter.

To ensure that music specifically written for one of the two SID versions can be played back correctly, bits 4-7 in 'flags' are used as stated above.

If bits 6-7 are set to Unknown then the second SID will be set to the same SID model as the first SID.

- Bits 8-15 are reserved and should be set to 0.

    +78    BYTE startPage (relocStartPage)

This is a v2NG specific field.

This is an 8 bit number. If 'startPage' is 0, the SID file is clean, i.e. it does not write outside its data range within the driver ranges. In this case the largest free memory range can be determined from the start address and the data length of the SID binary data. If 'startPage' is 0xFF, there is not even a single free page, and driver relocation is impossible. Otherwise, 'startPage' specifies the start page of the single largest free memory range within the driver ranges. For example, if 'startPage' is 0x1E, this free memory range starts at $1E00.

    +79    BYTE pageLength (relocPages)

This is a v2NG specific field.

This is an 8 bit number indicating the number of free pages after 'startPage'. If 'startPage' is not 0 or 0xFF, 'pageLength' is set to the number of free pages starting at 'startPage'. If 'startPage' is 0 or 0xFF, 'pageLength' must be set to 0.

The relocation range indicated by 'startPage' and 'pageLength' should never overlap or encompass the load range of the C64 data. For RSID files, the relocation range should also not overlap or encompass any of the ROM areas ($A000-$BFFF and $D000-$FFFF) or the reserved memory area ($0000-$03FF).

    +7A    BYTE secondSIDAddress

This is a v3 specific field. For v2NG, it should be set to 0.

This is an 8 bit number indicating the address of the second SID. It specifies the middle part of the address, $Dxx0, starting from value $42 for $D420 to $FE for $DFE0). Only even values are valid. Ranges $00-$41 ($D000-$D410) and $80-$DF ($D800-$DDF0) are invalid. Any invalid value means that no second SID is used, like $00.

    +7B    BYTE reserved

This is a 8 bit number and is reserved and should be set to 0.

    +7C    <data>

Version 2 and 3 of the SID header ends here. This offset is the start of the binary C64 data. See also 'loadAddress' for what the first 2 bytes of 'data' might indicate.

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