I came across another detail somewhat buried in the TPU. This relates to the register at $14FA.
I see in the code where $14FA is accessed to determine if ASR is active.
I am a bit fuzzy on all the three letter acronyms, not sure which are for what years and if some of them relate to the same issues. Perhaps some help here from those well versed in the history of E/PCMs? I think ASR (Automatic Slip Regulation), ASR (Acceleration Slip Regulation) and TCS (Traction Control System). In any case looking through the GM docs for the car, I will use ASR to describe this function.
ASR looks at the status of connector C1 (Red) pin 23 to determine if spark should be retarded in the cycle to reduce engine output. Bit 3 in register $14FA matches the input. The signal enters the PCM through the connector, is conditioned by passive components (R and C) and buffered by a comparator and connected to the TPU on pin 22. I looked at this and noted that many other bits in the register were also active and changing. Some investigation later and I find that these bits contain a snapshot of the inputs and outputs to the TPU. I did not do an exhaustive look at the register as code only accesses the one bit. In the short look at the register I did find the following bits and the inputs they represent:
BIT 2: FROM COMPARATOR: C1 RED P26
BIT 3: AUTOMATIC SLIP REGULATION
BIT 4: MASS AIR FLOW
BIT 5: VEHICLE ANTI-THEFT SYSTEM (VATS)
BIT 15: KNOCK DETECTED
Does anyone know what connector C1 (RED) Pin 26 was used for? This might be a B body or Corvette function? My PCM omitted resistors connecting the pin to the input. To find this input I needed to probe deeper in the circuit.
Another question: Does anyone know if the TPU uses the input pin internally or if it is just passed through to the register for software to look at?
-Tom
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