Cartridge header

[Tom]

Can anybody explain me, what the first four pointers (right after the cartridge identification word) in the cartridge header are good for ? Are these used by BIOS functions ? Is it safe to simply set them to 0 ?

[CPUWIZ]

Can anybody explain me, what the first four pointers (right after the cartridge identification word) in the cartridge header are good for ? Are these used by BIOS functions ? Is it safe to simply set them to 0 ?

961635[/snapback]

 

I don't think they are used.

 

http://atarihq.com/danb/files/CV-Tech.txt

[Tom]

Ok, I found a BIOS disassembly. They point to buffers in RAM which some BIOS functions use. If you don't call those particular BIOS functions, the pointers can contain *any* value.

 

(The whole point in this seems to be to let the programmer have control over where these buffers are placed, since they can be fairly large. You could probably even overlay some them.)

Edited November 7, 2005 by Tom

[Bruce Tomlin]

They're used by various routines in the BIOS. If you don't use those routines (many of which I'm not sure how you're supposed to use them), then it doesn't matter. Basically, you're supposed to point them to the RAM locations where you want certain tables stored.

 

From a disassembly I have (not sure where I got the variable names, probably I came up with them myself), the header is:

 

8000: Cart_Sig - AA55 = title screen, 55AA = no title screen

8002: RamSprtTab - RAM sprite attribute table pointer

8004: RAMSprtIdx - sprite index table pointer

8006: VDP_Temp - pointer to temp image storage (up to 40 bytes used)

8008: CtlState - pointer to controller state table (2 + 2x5 bytes)

800A: Cart_Start - start of cartridge code

800C: RST 08H

800F: RST 10H

8012: RST 18H

8015: RST 20H

8018: RST 28H

801B: RST 30H

801E: RST 38H

8021: NMI

8024: Cart_Title - Title string "LINE 3/LINE 2/yyyy"

[Tom]

This document contains a BIOS listing (original, not a commented disassembly ?):

http://www.geocities.com/newcoleco/cv-coding-guide.zip

 

Apparently the BIOS contains among other things sprite multiplexing routines.