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Sega SC3000 - 315-5031 vs Mitec 2Posted: Thu Apr 18, 2019 9:17 am
The Sega SC-3000 IC-2 is usually a Mitec 2 chip which is a custom gate array. It did things like combine the Z80 /IORQ with /WR and /RD to give /IOR and /IOW and combine /MREQ with /WR and /RD to give /MEMW and /MEMR.
I just popped my Yeno SC-3000 case open tonight because I was having some weird issues with my Megacart and instead of a Mitec 2 chip, it is labelled as a Sega 315-5031
I assume the 315-5031 is designed to be broadly compatible with the Mitec-2 chip, but I'm wondering if there are some slight timing differences.
Does anyone know anything about the difference between these chips or some history on them? I have opened quite a few SC-3000s but this is the first time I've seen anything other than a Mitec 2 in the IC2 position.
The Yeno still has the same Sega 1983 (171-5048) motherboard as my workbench PAL SC-3000 but maybe it was assembled a bit later. (There are other obvious differences like the RGB daughterboard, lack of RF modulator, some different components on motherboard due to different video system etc., but the IC2 is the one most likely to be causing me issues.)
The description in the Sega SC-3000 service manual for IC2 is:
Custom IC (gate array)
This has function to prevent RESET signal chattering and from CPU signal (/MREQ, /RD, /WR, /IORQ, /REFRESH, A6, A7, A14, A15) to generate CS (chip select) signals of SRAM, SGC, and VDP as well as to generate control signals of exterior ROM and exterior DRAM.