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duxthe1 · #15 10-04-2019, 08:27 PM

Another weekly progress report...

I've dug though some old wiring and realized I had a 55 pin CIS module harness with about 20" of wiring with the connector. With the harness connected, a bit of time spent trying to match functions to microcontroller pins, though not a lot of progress there. I did solder a 10 ohm resistor across the EHA wires to make a current measurement easy.

Perusing WIS on CIS and EZL functions I came across the info about the CIS trim resistor. We didn't get the CIS trim resistor here in the States, but select modules worldwide had the potential to change enrichment maps based on a selected resistance. My US harness isn't even populated for the contacts that the resistor connects to. I did however find that the trim resistor pin goes to the microcontroller's analog input pin 3. The interesting thing is that all 8 analog channels get read so in theory it may be possible to select one of the alternate maps, either with hardware or software.

Lastly I did a bit of poking around on another "973" module and determined that the EHA's microcontroller pin uses a pulsewidth to control the circuitry. 1kHz on the pin equates to 20mA EHA current. I recall somewhere in WIS mentioning that the CIS "switches polarity" of the EHA current referencing decel fuel cut. I think it may have been literal and there is likely a microcontroller pin that actually signals a switch to negative current on the EHA.

Lastly I drew out all of the special function registers that are initialized and populated them with the initial values as well as their functions.

It doesn't feel like a lot of progress this week but a fair amount of time was spent reading about and studying 8051 programming. A bit better familiarity with the microcontroller should help me understand what the software is actually doing. I've ordered one of the best books on the subject, but don't expect it until later next week.