How the 4A-GE ECU works

[firehawk]

Quote:I would imagine one EPROM contains all the program code and one will contain the mapping (the socketed one).

That's what I thought as well. I'll have to try to follow the address lines from the CPU to the EPROMs and PIA to see how they're mapped into the address space. The "001" EPROM appears to be 32Kbit, while the other one is only 16Kbit. It would seem possible that the code is mapped to $F000-$FFFF because the reset vector on 6800 series CPUs is at $FFFE:$FFFF. The lack of an external RAM chip on the board would suggest that the mystery ND chip might actually be a Hitachi 6301 or 6303.

This is actually getting so exciting that I probably have to remove both EPROMs from the board, then dump them and disassemble the code to satisfy my curiosity - It's been a while since I've done some proper reverse-engineering.

Quote:I am very surprised they use a cheap pressed ribbon cable connector to interconnect the two PCBs. I would have thought a direct soldered 0.1" pitch ribbon would have been more reliable and worth the extra expense. (i.e. that's what I use)

Indeed. The 3S-GTE ECU consists of two boards which are connected with a quite solid ribbon cable soldered directly onto the boards just as you described. The cable used by TRD, however, is more flexible so they may have chosen to use if they've thought that the two boards need to be often removed from the casing and put back. I can't, however, see why one would need to do this as the EPROMs are easily accessible after just removing the upper lid of the casing. Maybe they had originally thought that the piggyback board would be mounted in the casing component side down.