NES-CNROM RAM cartridge - HOWTO

[Quietust]

NES-CNROM-256-05 RAM cart (for use with CopyNESW)

Parts needed:
* Two 62256 (32KB SRAM) chips
* Two (or three) SPDT switches (Mirroring, PRG write protect; CHR write protect is optional - I didn't use it in mine)

PRG RAM:
* Bend up pins 1, 20, 22, and 27
* Connect pin 1 (RAM A14) to hole 27 (CPU A14)
* Connect pin 20 (RAM /CE) to hole 22 (CPU /CE)
* Connect pin 22 (RAM /OE) to hole 20 (GND)
* Connect pin 27 (RAM /WR) to the 'COM' pin of the PRG switch
* Connect the 'A' pin of the PRG switch to CPU R/W (74LS161, pin 9)
* Connect the 'B' pin of the PRG switch to VCC

CHR RAM:
* Bend up pins 1 and 27
* Connect pin 1 (RAM A14) to hole 27 (74LS161 latch output Q1)
* Connect pin 27 (RAM /WR) to the PPU /WR pad on the cart edge (you will need to scrape off the solder mask and cut a notch in the case to make room for the wire) OR connect it to another switch (and connect the remaining lines accordingly)

Mirroring:
Connect VRAM A10 (the top half of either mirroring pad) to the 'COM' pin of the Mirroring switch
Connect PPU A10 (the bottom half of the 'V' pad) to the 'A' pin of the Mirroring switch
Connect PPU A11 (the bottom half of the 'H' pad) to the 'B' pin of the Mirroring switch


Pictures of my CNRAM cart (warning - a bit messy):
http://www.qmtpro.com/~nes/misc/cart_edge.jpg
http://www.qmtpro.com/~nes/misc/cart_front.jpg
http://www.qmtpro.com/~nes/misc/cart_back.jpg