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

A78 Header Fields

0000	01	41	54	41	52	49	37	38	30	30	00	00	00	00	00	00	.ATARI7800......
0010	00	43	6f	6d	6d	61	6e	64	6f	00	00	00	00	00	00	00	.Commando.......
0020	00	00	00	00	00	00	00	00	00	00	00	00	00	00	00	00	................
0030	00	00	02	00	00	00	03	01	01	00	00	00	00	00	00	00	................
0040	00	00	00	00	00	00	00	00	00	00	00	00	00	00	00	00	................
0050	00	00	00	00	00	00	00	00	00	00	00	00	00	00	00	00	................
0060	00	00	00	00	41	43	54	55	41	4c	20	43	41	52	54	20	....ACTUAL CART
0070	44	41	54	41	20	53	54	41	52	54	53	20	48	45	52	45	DATA STARTS HERE

color	purpose	size
	header version	1 byte
	ATARI7800 magic-text	16 bytes
	cart title	32 bytes
	rom size without header	4 bytes
	cart type	2 bytes
	controller 1 type	1 byte
	controller 2 type	1 byte
	TV type	1 byte
	save device	1 byte
	reserved
	expansion module	1 byte
	header end magic-text	28 bytes

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.

        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