Capcom Commando Custom Chip

SamWhiskey

Well-known member
Joined
Jun 19, 2015
Messages
1,031
Reaction score
300
Location
NRW, Germany
Hi Folks, :)

My Capcom Commando PCB ist missing the Custom @ 10M

I read somewhere on the Internet, there's a replacement circuit (maybe from a BL?) available. Can't find it anymore. :(

Has anyone a schematic or photos of this replacement?

Greetings
Sam
 
Is this a riddle? I'm confused. That has to be the most vague description of a chip location. Hint, if you ask for help it does help to be less cryptic.
 
:confused:

There is only one custom chip on commando PCBs, and as in post#1 stated at Position 11M. It has 48 Pins (2 sockets with 24 pins soldered in) if this helps more. ;)

It has it's own page in the manual (page 33).

The label on the chip is normally scratched off (never saw a pic with label).

That's all avaliable Information.

So where is the confusion? ;)
 
Last edited:
Here we go: :p

attachment.php
 
Not clear from the schematics what the chip does - but I think it decrypts the opcodes going to the CPU?

This is in mame source about the bootleg, I assume it's how the bootleg mimics the custom chip.


/* There's a 16L8 PAL (with a 74LS245 and a 74LS08) on a tiny sub-board between the CPU1 ROMs
and the CPU1 (a Z80 compatible NEC D780C-1). This sub-board is plugged on what seems to be
a ROM socket.

PAL16L8 (SWELT-019A)

Pin 1 - Pin 12 of 27256 (D1) and Pin 3 of 74LS245 (A2) (Input)
Pin 2 - Pin 13 of 27256 (D2) and Pin 4 of 74LS245 (A3) (Input)
Pin 3 - Pin 15 of 27256 (D3) and Pin 5 of 74LS245 (A4) (Input)
Pin 4 - Pin 8 of 74LS08 (Input)
Pin 5 - Pin 17 of 27256 (D5) and Pin 7 of 74LS245 (A6) (Input)
Pin 6 - Pin 18 of 27256 (D6) and Pin 8 of 74LS245 (A7) (Input)
Pin 7 - Pin 19 of 27256 (D7) and Pin 9 of 74LS245 (A8) (Input)
Pin 8 - Pin 6 of 74LS14 (Input)
Pin 9 - Pin 11 of 74LS08 (Input)
Pin 10 - Ground
Pin 11 - Pin 22 of Z80 (~WD) and Pin 1 of 74LS245 (DIR) (Input)
Pin 12 - Pin 19 of 74LS245 (~OE) (Output)
Pin 13 - Pin 13 of Z80 (D7) (Input?, Output)
Pin 14 - Pin 10 of Z80 (D6) (Input?, Output)
Pin 15 - Pin 9 of Z80 (D5) (Input?, Output)
Pin 16 - Not Used (Input?, Output)
Pin 17 - Pin 8 of Z80 (D3) (Input?, Output)
Pin 18 - Pin 12 of Z80 (D2) (Input?, Output)
Pin 19 - Pin 15 of Z80 (D1) (Output)
Pin 20 - VCC

------------------------------------------------------------------------------

Pin 14 of Z80 (D0) to Pin 11 of 27256 (D0)
Pin 7 of Z80 (D4) to Pin 16 of 27256 (D4)
 
So you got me thinking more about this over lunch ;)

So I believe the custom chip sits between the CPU data bus and everything else (or at least main RAM and ROM). When the M1 signal from the CPU is high it just passes through the data. When the M1 signal is low it swizzles D1-D3 to be D5-D7 and vice versa. Thus the opcode are 'decrypted'.

If you were really set on fixing this, you could do 3 things:

1: Just making a pass-through in the custom chip socket, and then make a custom ROM with the opcodes already decrypted. (Which is a bit harder than it sounds as you'd have to trace all program paths).

2: Make a sub-board containing another set of program ROMS and put it in the custom chip socket. This set of program ROMs is entirely swizzled D1-D3/D5-D7 (for opcodes). When M1 is low you select the 'opcode set' else select the regular set.

3: Burn a PAL/GAL from the MAME bootleg set and make the connections above (you can clearly see the swizzle and D0/4 being passthrough).

Got all that? :)

(Edit - no, don't do number 2 - instead make the passthrough, put in double size program ROMs, put standard in bottom half, and decrypted in top half - then use M1 to drive the high address line).
 
Back
Top Bottom