The donor cart
Crisis Force is one of the game from Konami that uses the famous VRC-4 chip. So the donor should also have this chip. The other characteristic of the cart is that it needs 2KB of SRAM (15ns access speed) in order to work.
A cart that has both SRAM and VRC4 is Gradius 2 so it makes it a perfect donor.
Two EPROMs are needed with 128 KB for CHR and PRG. There are no 28 pins EPROM for this size, so a 32 pin EPROM will be used.
A 27C010, 27C020 or 27C040 would work here. If a bigger EPROM is used, the PRG/CHR file need to be modified to match the size of the EPROM. For instance to make it on a 27C040:
cat crisis.prg crisis.prg crisis.prg crisis.prg > crisis_ready.prg
This guide is inspired from this tutorial that aims to convert Tiny Toons donor into Akumajō Special: Boku Dracula-kun. Thanks to the help of the author of this article I managed to get the right wiring.
There are different variants of the VRC4. Crisis force needs VRC4e while Gradius2 has VRC4b. Those are the differences.
VRC4b, PCB 351406, mapper 25
(fr) CPU A0 -> |03 38| -> PRG A15 (r) (fr) CPU A1 -> |04 37| <- CPU A12 (f)
VRC4e, PCB 352396, mapper 23
(fr) CPU A3 -> |03 38| -> PRG A15 (r) (fr) CPU A2 -> |04 37| <- CPU A12 (f)
So it will be needed to put wires to connect the VRC4 to A3 and A2.
On both EPROMS:
Lift pins: 1, 2, 24, 31, 32
Place the EPROM PRG is on the left and CHR on the right.
Do the wiring as follows:
- Pin 1 stays up and unconnected
- Pin 2 goes to hole 24 on the PCB
- Pin 24 goes to GND
- Pin 31 and 32 goes to 5V
On the VRC4:
Lift pins 3 and 4.
Connect VRC4 pin 3 to PRG pin 9 (A3)
Connect VRC4 pin 4 to PRG pin 10 (A2)