History

The Idea

One sunday afternoon we started playing with the idea building a developer cartridge for the SNES. The basic idea was to upload the rom image to an SRAM and connect the SRAM to the SNES address and data bus.

To understand of how the SNES workds we started with building a rom dumper. We actually used a self build FTDI based JTAG adapter that was lying around. Connected the 8 bit port A of the FTDI to the data bus of the ROM and used the port B to drive a counter.

At the same time we did some research what kind of cartridges were used in the wild for the SNES. To get an better idea how addressing of the different cartridges worked. So we ordered a couple of SNES games on ebay and analysed the PCBs

Proof Of Concept

Next step would be to run a small rom image from a single SRAM chip. We figured that we need an address counter logic to save IOs. Otherwise we would have never managed to use an AVR, which lags that kind of number of IOs for such a projects. We started with using an STK500 to host the cpu which was attached to a breadboard holding on 512KB SRAM and the counters for the memory addressing. On the SNES side we plugged a multigame adapter into the SNES to piggyback a CIC circuit and re-routed the address and data lines to the breadboard. That was a real mess of wires...We wrote a little SNES rom, displaying a Mario sprite. Uploaded the rom file and used an actual hardware switch to give controll about the buses from AVR to the snes.

Prototype PCB

PCB prototype was produced by pcbpool. Using 32Mbit Sram, AVR 644 and a FTDI for a debug console.