SGROM with no CHR RAM is equal too what PCB class?

SGROM with no CHR RAM is equal too what PCB class?
by nintendo2600 on 2009-12-06 (#53638)

Hey,

I got a defender of the crown by accident today (thoought it was SN-ROM, not SG-ROM my bad I know) but anyhow what I was wondering is with the CHR RAM removed what kinda PCB would this board be equal too?

Just a normal MMC1 board? As in I could wire up an EPROM to the CHR spot the same as any old MMC1 board? Also is the CHR on this board limited to a size or am I good to go on putting a 1 or 2 meg chip on there (obviously with the right wiring scheme).

Thanks,

N2600

by tepples on 2009-12-06 (#53644)

MMC1 IC pinout from rom.txt
A known SNROM game: The Legend of Zelda (PCB pics at bootgod)
The SGROM wiki page implies that if you take the PRG RAM off an SNROM board, you have SGROM.

Take the CHR RAM off too, and you have nothing. The CHR ROM bank bits out of the MMC1 just lead straight off the top of the board, so you can't use anything bigger than 8 KiB without rewiring directly to the MMC1.

by nintendo2600 on 2009-12-07 (#53662)

tepples wrote:
MMC1 IC pinout from rom.txt
A known SNROM game: The Legend of Zelda (PCB pics at bootgod)
The SGROM wiki page implies that if you take the PRG RAM off an SNROM board, you have SGROM.

Take the CHR RAM off too, and you have nothing. The CHR ROM bank bits out of the MMC1 just lead straight off the top of the board, so you can't use anything bigger than 8 KiB without rewiring directly to the MMC1.

OK thanks. Looks like I bought myself a dud.

by tokumaru on 2009-12-07 (#53664)

But the MMC1 is a big chip, it should be easy to solder wires directly to it. If it was an MMC3 it would much harder because the pins are so small.

by nintendo2600 on 2009-12-08 (#53730)

tokumaru wrote:
But the MMC1 is a big chip, it should be easy to solder wires directly to it. If it was an MMC3 it would much harder because the pins are so small.

Too much work for so little reward IMO. Maybe someday if I'm bored and feeling adventurous I'll have a crack at it I suppose.

by tokumaru on 2009-12-08 (#53732)

nintendo2600 wrote:
Too much work for so little reward IMO.

IMO, it's very little additional work compared to what you'd have to do anyway on a board which already has CHR-ROM. Desoldering the original chips, comparing pinouts, bending pins, cutting traces and adding wires is something you'll have to do anyway. Wiring the higher address lines directly to the MMC1 is just like, 5 more wires or so, directly from the ROM chip to the mapper chip, not very hard at all.