Hi, I`m planning to make eprom based flash cart and I need some help and suggestions from you guys. I want to modify Dr mario (the upper one in the pic) and super mario cartridge. I will make my own eprom programmer,the schematic is very simple but it can only flash 27(c)128,27256 and 27512 eproms. I already have a few of 256 and 512 kbits eprom ICs. So, can I use these eproms by just replacing with mario or Dr Mario ROMs without any modification?
and here`s the programmer schematic....
Super Mario is a NROM cartridge. There are pin compatible EPROM for it I believe. But Dr Mario is MMC1 and supports up to 256k PRG and 128K CHR I believe. There are no pin compatible eprom or flash roms. You have to do some rewiring. There should be details on this site on "building reproduction cartridges" which is the same thing you are doing basically.
Dr Mario uses SEROM, and by default this board only accept small ROMs with standard EPROM pinouts I assume (at least this is the case of TEROM, so it's very likely to be the case on SEROM, which I can't verify because I only have Dr.Mario on the GameBoy).
In short, SLROM have non-standard pinouts, but SEROM have standard ROM pinouts.
It should be possible to have bigger EPROMs by adding wires, but you'll have to bend the 4 border-pins of your 32-pin chips to have them fit in the 28-holes board, and do some minor additionnal rewiring. This is in other words turning SEROM to SLROM.
yes, dr mario is serom (it`s printed on the pcb), the ICs I want to use are identical by number of legs (27c256 or 512), I guess 64/128 KB is quite enough... I`ll have to find original rom pinouts to compare.... but I still wonder if nes will read this sizes because dr mario is about 42KB....
Dr Mario has two 32Kbyte ROMs. SEROM accepts 32K PRG maximum and 64K CHR maximum. That would be your limitations for it. I don't know if a 64kbyte eprom has the same pinout or not, maybe it does. The 32K eprom should be the same though.
http://nesdevwiki.org/wiki/SxROM
If you want to turn the SEROM board to SBROM (aka allowing 64kb PRG and 64kb CHR, the maximum available if you only want to deal with 28-pins chips only) you'll only have to disconnect pin 1 to VCC and tie it to PRG A15 on the MMC1, which should be extremely simple to do.
Why Nintendo did different boards for SEROM and SBROM to me is a complete mystery. I see no reason why a 32kb chip shouldn't work on SBROM (without rewiring). The same question remains for SCROM and SHROM, which seems also identical exept for pin 1 of the PRG.
thanx for all the info.... I`ll try something but first have to build eprom programmer and see if it`s working....
I would suggest using FlashROMs, and a better (supported and/or capable) programmer. Unless you don't mind using an EPROM eraser, or just want to program each chip once.
Shouldn't Flash chips hold up better/longer? I hear issues of EPROMs getting partially erased over a long time. But I've never heard of long time issues with flash other than wearing out after hundreds of thousands of flash cycles.
I`m planning to use both erasable and OTP eproms, 27c256 I already have are UV erasable.....I`m just experimenting now (never flashed an eprom before) and if everything goes ok I will buy some descent flash programmer and make flash cart for SNES too....
MottZilla wrote:
Shouldn't Flash chips hold up better/longer? I hear issues of EPROMs getting partially erased over a long time. But I've never heard of long time issues with flash other than wearing out after hundreds of thousands of flash cycles.
Flash chips won't hold their program forever either, they just haven't been around long enough for it to happen. EPROMs are supposedly good for 20+ years, I imagine it varies. I think Color Dreams or some other unlicensed carts used OTP EPROMs.
Flash is easier to program though (and 29F is self-programming, NES or anything can do it).