View source for A78 Header Specification

==History and Purpose==

The A78 header was originally created by Dan Boris, in tandem with his A7800 emulator. The header, which is added to the beginning of ROM images, serves to tell the emulator which hardware should be present for the game to run correctly.

The format has since been expanded to incorporate new hardware, and is now being used by multiple emulators and the Concerto 7800 flash cart.

==A78 Header Fields==

 {|  style="float:left;"
  |+A78 Header Fields
 ! 0000 || style="background-color: #fc8;" | 01 || style="background-color: #fcf;" | 41 || style="background-color: #fcf;" | 54 || style="background-color: #fcf;" | 41 || style="background-color: #fcf;" | 52 || style="background-color: #fcf;" | 49 || style="background-color: #fcf;" | 37 || style="background-color: #fcf;" | 38 || style="background-color: #fcf;" | 30 || style="background-color: #fcf;" | 30 || style="background-color: #fcf;" | 00 || style="background-color: #fcf;" | 00 || style="background-color: #fcf;" | 00 || style="background-color: #fcf;" | 00 || style="background-color: #fcf;" | 00 || style="background-color: #fcf;" | 00 || <tt>.ATARI7800......</tt>
 |-
 ! 0010 || style="background-color: #fcf;" | 00 || style="background-color: #acf;" | 43 || style="background-color: #acf;" | 6f || style="background-color: #acf;" | 6d || style="background-color: #acf;" | 6d || style="background-color: #acf;" | 61 || style="background-color: #acf;" | 6e || style="background-color: #acf;" | 64 || style="background-color: #acf;" | 6f || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || <tt>.Commando.......</tt>
 |-
 ! 0020 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || style="background-color: #acf;" | 00 || <tt>................</tt>
 |-
 ! 0030 || style="background-color: #acf;" | 00 || style="background-color: #faa;" | 00 || style="background-color: #faa;" | 02 || style="background-color: #faa;" | 00 || style="background-color: #faa;" | 00 || style="background-color: #ffb;" | 00 || style="background-color: #ffb;" | 03 || style="background-color: #8fc;" | 01 || style="background-color: #caa;" | 01 || style="background-color: #8c8;" | 00 || style="background-color: #c8c;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #aac;" | 00 || <tt>................</tt>
 |-
 ! 0040 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || <tt>................</tt>
 |-
 ! 0050 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || <tt>................</tt>
 |-
 ! 0060 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #eee;" | 00 || style="background-color: #cf8;" | 41 || style="background-color: #cf8;" | 43 || style="background-color: #cf8;" | 54 || style="background-color: #cf8;" | 55 || style="background-color: #cf8;" | 41 || style="background-color: #cf8;" | 4c || style="background-color: #cf8;" | 20 || style="background-color: #cf8;" | 43 || style="background-color: #cf8;" | 41 || style="background-color: #cf8;" | 52 || style="background-color: #cf8;" | 54 || style="background-color: #cf8;" | 20 || <tt>....ACTUAL CART </tt>
 |-
 ! 0070 || style="background-color: #cf8;" | 44 || style="background-color: #cf8;" | 41 || style="background-color: #cf8;" | 54 || style="background-color: #cf8;" | 41 || style="background-color: #cf8;" | 20 || style="background-color: #cf8;" | 53 || style="background-color: #cf8;" | 54 || style="background-color: #cf8;" | 41 || style="background-color: #cf8;" | 52 || style="background-color: #cf8;" | 54 || style="background-color: #cf8;" | 53 || style="background-color: #cf8;" | 20 || style="background-color: #cf8;" | 48 || style="background-color: #cf8;" | 45 || style="background-color: #cf8;" | 52 || style="background-color: #cf8;" | 45 || <tt>DATA STARTS HERE</tt>
 |-
 |}

 {| style="float:left; margin-left: 30px;"
 ! color !! purpose !! size
 |-
 | style="background-color: #fc8;" | &nbsp; || header version || 1 byte
 |-
 | style="background-color: #fcf;" | &nbsp; || ATARI7800 magic-text || 16 bytes
 |-
 | style="background-color: #acf;" | &nbsp; || cart title || 32 bytes
 |-
 | style="background-color: #faa;" | &nbsp; || rom size without header || 4 bytes
 |-
 | style="background-color: #ffb;" | &nbsp; || cart type || 2 bytes
 |-
 | style="background-color: #8fc;" | &nbsp; || controller 1 type || 1 byte
 |-
 | style="background-color: #caa;" | &nbsp; || controller 2 type || 1 byte
 |-
 | style="background-color: #8c8;" | &nbsp; || TV type || 1 byte
 |-
 | style="background-color: #c8c;" | &nbsp; || save device || 1 byte
 |-
 | style="background-color: #eee;" | &nbsp; || reserved || &nbsp;
 |-
 | style="background-color: #aac;" | &nbsp; || expansion module || 1 byte
 |-
 | style="background-color: #cf8;" | &nbsp; || header end magic-text || 28 bytes
 |}

<div style="clear:both;"></div>

==Adding an A78 Header to Source Code==

To add an A78 header to your DASM source code, you can add or include the header at the start of your source, and adjust the fields to encode the hardware your game requires.

<pre>
        SEG     ROM
HEADER  ORG     ROMTOP-128
        DC.B    1  ; 0   Header version     - 1 byte
        DC.B    "ATARI7800"     ; 1..16  "ATARI7800   "  - 16 bytes
        DS      7,32
        DC.B    "Your Name Here"; 17..48 Cart title      - 32 bytes
        DS      HEADER+49-.,0
        DC.B    $00,$00,256->ROMTOP,$00; 49..52 data length      - 4 bytes
        DC.B    $00,$00  ; 53..54 cart type      - 2 bytes
    ;    bit 0 - pokey at $4000
    ;    bit 1 - supergame bank switched
    ;    bit 2 - supergame ram at $4000
    ;    bit 3 - rom at $4000
    ;    bit 4 - bank 6 at $4000
    ;    bit 5 - supergame banked ram
    ;    bit 6 - pokey at $450
    ;    bit 8-15 - Special
    ;   0 = Normal cart
        DC.B    1  ; 55   controller 1 type  - 1 byte
        DC.B    1  ; 56   controller 2 type  - 1 byte
    ;    0 = None
    ;    1 = Joystick
    ;    2 = Light Gun
        DC.B    0  ; 57 0 = NTSC 1 = PAL
        DC.B    0  ; 58   Save data peripheral - 1 byte (version 2)
    ;    0 = None / unknown (default)
    ;    1 = High Score Cart (HSC)
    ;    2 = SaveKey
        ORG     HEADER+63
        DC.B    0  ; 63   Expansion module
    ;    0 = No expansion module (default on all currently released games)
    ;    1 = Expansion module required
        ORG     HEADER+100      ; 100..127 "ACTUAL CART DATA STARTS HERE" - 28 bytes
        DC.B    "ACTUAL CART DATA STARTS HERE"
ROMTOP  ORG     $8000
</pre>