I plan to make devcarts out of some MMC1 and MMC3 boards that use the 28-pin 128kb mask ROM for PRG. The chips I want to use are 512kb flash ROMs, wich have 32 pins.
Although the mask ROM has only 28 pins, the other 4 holes seem to be present in the boards. My question is: are the extra holes "functional"? Or should they be ignored and only the lower 28 pins should be used in the rewiring process?
Thanks for the help.
I use the extra pins. Some are correct such as the Vcc. Others such as the high address lines are not. I cut the incorrect traces and connect the socket pins with wire wrap.
OK, thanks. And I have another question... If a board uses a 256kb chip, for example, there is no easy way to use more than that, right? Or are any boards ready for use with larger chips, even though they don't?
EDIT: I'm talking about a TSROM board, SMB3. Is it possible to use 512kb PRG and 256kb CHR with this board? Thanks.
http://www.tripoint.org/kevtris/mappers ... TSROM.html
TSROM is designed for max. 512 PRG and 256 CHR.
http://www.tripoint.org/kevtris/nes/nestuff2.txt
Take a look at the pinouts of the mapper chips. The MMC3 has A18 for PRG (512Kb) and A17 for the CHR (256KB). So any MMC3 cartridge can handle 512 Kb PRG and 256 Kb CHR. Just remember to connect the high address pins of the EPROM's to the corresponding pins of the mapper chip. I've done this on all my devcarts so they can all handle the maximum ROM capacity for the mapper. Conversely on the mapper 0 and 3 carts, I grounded some of the higher EPROM address pins so I could use the 27C512 which is cheaper and more easily available than the 27C64 and 27C128.
Great, thanks! Is that also true for MMC5 carts? I mean, can any MMC5 cart address up to 1MB of PRG and 1MB of CHR, as stated on that document (nestuff2.txt)? That's a pretty high limit...
EDIT: You said that the high address lines are not correct (in your first reply). But in relation to what? Are they not consistent with 32-pin 256kb or 512kb MASK ROMs? Any TLROM board can also be rewired to use 512kb PRG and 256kb CHR?
Thanks, and sorry if I look stupid, but I must be sure of those things 'cause I don't want to ruin any other carts. Thanks again!
Any MMC3 cartridge can use 512 PRG & 256 CHR (unless it has CHR-RAM). Just pay special attention to the EPROM pinouts and check where the 1,2, 22, 24, 31,32 ROM pins on the cartridge connect to. Then make sure they connect to the correct pins (A16, A17, A18, /CE, /OE) of the MMC3 chip or the NES edge connector.
Holes in MMC1 cartridge are definitely usefull, since most MMC1 boards are designed to be able to have 256kb PRGROM, wich have 32 pins.
However, I think this doesn't apply to SAROM, SFROM, and maybe others.