nesdev.com

I'm curious if anyone has had problems (or success) getting a NES-NROM-256 game running on the ReproX board. I ordered some of the boards and EPROMs from game-tech, and I've successfully created Battletoads, and Dig Dug repros. I created a NROM test board with sockets, which I used successfully for Dig Dug. I cannot, however, get a Super Mario Bros (NROM-256) repro working. I'm trying to get a SMB hack (of my own creation as a present for my daughter) working, I even tried regular, unaltered SMB (verified that CRC32 on each ROM image matches the bootgod records) and it doesn't work. It just gives me a grey or green screen. I've doubled (quadrupled, etc) the ROM images to fit the chips. I've tried both the AM27C128 and the AM27C020 chips for the CHR. I switched the mirroring. I checked the datasheet for the AM27C020, and it allows pin 1 pulled high or low. I chose high which worked for the Battletoads repro. I've polished the pins on the old EPROMs, verified the data, tried multiple different EPROMs. I'm either really unlucky, or I am missing something.

I did some further tests and my NROM socketed test ReproX board can run Dig Dug and Championship Lode Runner, which are both NROM-128, but can't run Super Mario Bros or Chubby Cherub, which are NROM-256. This page suggests that the mirroring is different: http://wiki.nesdev.com/w/index.php/Programming_NROM and that NROM-128 games mirror at $C000 and $8000 but generally run from $C000-$FFFF range while NROM-256 run only from $8000-$FFFF. If the PCB, as configured for NROM, only maps the PRG ROM to $C000, then only NROM-128 games would work--which is what seems to be happening. Or, possibly, one of the jumpers already handles this, and I really suck at soldering.