Mapper type?

sepi · Post by **sepi** » Tue Nov 15, 2005 9:14 am

Hi!
I found a weird unlicenced game named "Olympic I.Q." by Sachen, i'm trying to figure out which mapper it's using. it has 32k PRG-ROM (27C512) and (at the moment) unknown size of VROM, mapper itself is a 74LS374. Could this be a CNROM (VROM switch) clone?
- sepi

Quietust · Post by **Quietust** » Tue Nov 15, 2005 12:45 pm

That would be iNES mapper #243 - the "74LS374N" mapper is NOT a 74LS374, but a custom mapper chip labeled "74LS374N" to deliberately mislead anyone who might want to dump the game or create duplicate cartridges.

Incidentally, the PRG ROM is 64KB and CHR ROM is 32KB.

sepi · Post by **sepi** » Wed Nov 16, 2005 6:32 am

Hmm, i thought that 27C512 was size of 32kB...

Is there any information available from this custom chip? (i couldn't find any) is it a just plain mapper? or does it have some sort of encryption scheme?

i'm planning to remove chips from the board and dumping them with EEPROM tool.

Quietust · Post by **Quietust** » Wed Nov 16, 2005 12:13 pm

The chip functions similarly to an MMC3, with registers at $4100 and $4101 (and 4300/4301, 4500/4501, ..., 5D00/5D01, 5F00/5F01). It is NOT a plain mapper, though Sachen certainly wanted you to think so (and cause you to produce a nonfunctioning cartridge). For the record, Olympic IQ has been dumped by Kevin Horton, though I don't know if the ROM image is in circulation.

A 27C512 is 512Kbit, or 512 / 8 = 64KB.

sepi · Post by **sepi** » Thu Nov 17, 2005 2:56 am

Well, i have to admit that the Sachen has really used a quite unusual copyright protection scheme here

Thank you very much, Quietust.