How the 4A-GE ECU works

[JMR_AW11]

firehawk Wrote:On the ignition map, how does the 8-bit value correspond to actual ignition advance in degrees? Is it simple 0.8 fixed-point arithmetic, ie. the advance = max_advance*(cell_value/255)? If this is the case, have you determined what's the maximum advance in degrees (excluding the advance set mechanically from the distributor)?

Edit: man, I should refresh the browser window to see if there has been any more replies since I opened the thread.

You might also be interested in this;

http://www.r5r.net/gallery/album14

It's the TRD Group-A ECU used in circuit racing and rallying in the 80s and we're currently running our AE82 race car with the unit shown in the pictures. It's been build "on top" of the standard ECU similarly as we've discussed here. The piggyback board appears to have, in addition to some standard logic chips, an unknown Nippon Denso CPU (151801-1230? MC6800 clone?), a Hitachi HD46821 PIA (MC6820 clone) and two EPROMs (one marked 001, the other "RALLY4" "84.11.9" "E8" "5985"). I've been itching to dump out the contents of the socketed EPROM to see what I could find in there but my teammate doesn't want me to break our precious ECU.

That is very interesting to see that ECU.
I would imagine one EPROM contains all the program code and one will contain the mapping (the socketed one).

Unless you dump out both EPROMS and trace through the program code you are never going to find out which maps do what. If you ever dump out the EPROMs then I would be keen to see the contents of both EPROMs.

(Unless of course you already have this map info direct from TRD)

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)

BTW
If your ECU ever fails then I could repair it for you.