Activision bank switching logic.

[santosp]

Hello.

Can anyone know about the Activision's memory bank switching method? I mean how it handle the logic on its cartridge as to work.

The sure is that drive the latch using A0,A1,A2 address lines, in relation to Atari which use the data lines D0,D1,D2. Also make use of the A13 line.

 

I see cause the 2 known games work on Cuttle Cart and some emulators, so I believe that logic has been decoded.

 

Any help?

[CPUWIZ]

Double Dragon and Rampage have a very wierd bankswitchingscheme (78AC). It has 8 16K banks (0-7) that get mapped in at$a000-$dfff. Write accesses to addresses above $ff80 triggerthe bankswitching. This sets the bank according to the lownibble of the address. So a write to $ff80 maps in bank 0,a write to $ff81 maps in bank 1, etc. The games only useaddresses $ff80-$ff87, so I'm not sure if other addressestrigger the bankswitching too.If we are assuming that a bank reaches from $a000-$dfff,then the rest of the ROM space looks like this:$4000-$5fff second 8kb of bank 6$6000-$7fff first 8kb of bank 6$8000-$9fff second 8kb of bank 7$e000-$ffff first 8kb of bank 7

 

[santosp]

Yes I have read in the past this note from Ekchard Stolberg, but have you try if it work on some construction of yours?

[CPUWIZ]

No, I am not interested in making Activision repros, but it seems pretty straight forward to me. Looking at the connections of the PLD, the description isn't quite accurate, since it isn't touching the entire address range, only A13, A14 & A15 are inputs, so decoding is a bit more loose than $FF80-$FF87.

[santosp]

Yes plus A0, A1, A2.

[CPUWIZ]

Those 3 are just to latch the output address, or in other words, select bank 0 - 7.

[santosp]

The sure is that drive the latch using A0,A1,A2 address lines, in relation to Atari which use the data lines D0,D1,D2. Also make use of the A13 line.

 

 

Yes we agree. I just mentioned cause it have more than 3 address inputs.

Edited March 14, 2014 by santosp