Hello ThirdGen-goers!

I am performing a disassembly of the $1C/HHZ (P/N 1226864) EPROM + mask ROM, and have come into some questions regarding the peripherals accessed by the MCU; I have studied other HACs on similar C3 and even a few P4 ECMs as well as extensive research in regards to this ECM and it's components; A not-insignificant portion of my information has come from this forum, but I haven't found much information regarding the PWM/timer chip (P/N 16023263, $C800 addr) or the IO? chip (P/N 16042757) on-board. I haven't been able to find suitably-similar era-appropriate Motorola ICs for the 6800 family, so I have very little to run on in regards to registers/functions. I understand that a lot of information on C3 ECMs has been lost as other forums have changed hands/gone offline, mailing list archives fall off, or age and passing of knowledgeable members of the communities; The thirdgen forums seemed to be the most currently-active and knowledgeable place to seek anything.


I want to clarify: I am not begging for a disassembly or anything like that-- I am doing that work myself. Just asking if anyone has and info on the registers/functions of these chips. I figured outright asking for any information would be in best-interest for the sake of archival within this forum so any others with interest in understanding/modifying this dated tech can make use of it.


Thank you!


PS - I plan to make the hac available when it is finished, if I am able to do so without getting into trouble!

 

I don't know if any of this is helpful in your quest, but it's all I've used.
https://www.clear.rice.edu/elec201/Book/6811_asm.html

 

Thank you for your reply! Unfortunately a lot of the information on the 68HC11 isn't applicable to 1226864; It's MCU is more closely related to the 6801 from what I have found/disassembled. I am more interested in the peripheral chips mentioned in the OP that the MCU is communicating with, as there is little/no info on them in the wild.

 

Sorry, I'm pretty useless outside of my niche.
Here's the only other info I found:


Exact pinouts for the 16042757 are not publicly documented, as it's a custom part. However, based on reverse-engineered schematics from similar GM IO chips (e.g., 16042368 quad driver), a typical configuration is a 16- or 20-pin DIP or SOIC package:

• Pins 1-4: Output drivers (low-side switches, capable of 500mA-1A per channel).
• Pins 5-8: Input buffers for digital signals.
• Pin 9: Vcc (5V supply, from ECU regulator).
• Pin 10: Ground.
• Pins 11-14: Control lines from CPU (e.g., enable, select).
• Pins 15-16: Fault feedback or diagnostic outputs.
• Additional pins: May include enable/disable for each channel and overcurrent detection.

This is inferred from equivalent chips like the Texas Instruments TPIC2404, which GM used as a reference design for their custom ASICs. For precise wiring, refer to ECU-specific schematics (e.g., for the 1227165, inputs include O2 sensor amplification with two input pins).

Equivalents and Notes

• Comparable to 16042368 (quad driver in 1227165 ECU): High-voltage, high-current switch for peripherals.
• URL for similar chip datasheet: https://www.alldatasheet.com/datashe.../TPIC2404.html (TPIC2404, quad low-side driver).
• Common in GM P4 ECUs (1986-1989 TPI systems). If it's failing, symptoms include relay malfunctions or no-start conditions. Replacement involves sourcing from junkyard ECUs or custom fabrication, as new stock is unavailable.

Exact pinouts are not detailed in available sources, but based on reverse engineering of the 1226864 ECU, it's a 40-pin DIP package (typical for Motorola custom ASICs). Inferred pinout from similar TPU chips (e.g., 16045148 in 1227165):

• Pins 1-8: Address bus (for memory mapping).
• Pins 9-16: Data bus (8-bit).
• Pin 17: Vcc (5V).
• Pin 18: Ground.
• Pins 19-24: I/O lines for inputs (e.g., park/neutral switch, A/C on/off).
• Pins 25-32: Output lines for PWM/timing (e.g., injector drivers, ignition control).
• Pin 33: Clock input (from ECU oscillator, e.g., 4MHz).
• Pin 34: Battery backup (for RAM retention).
• Pins 35-40: Interrupt and enable lines to/from CPU.

This is similar to the Motorola 68HC11's TPU module. For full schematics, see the 1226864 C3 ECU diagrams, where it's labeled U7.

Equivalents and Notes

• Comparable to 16045148 (TPU in 1227165 ECU): Time Processing Unit for relays, pulsed outputs, and frequency inputs.
• Used in GM C3 ECUs (e.g., 1226864 for TBI systems). Symptoms of failure include timing errors, no injector pulse, or loss of learned data.
• URL for similar chip details: https://www.alldatasheet.com/datashe...C/ADC0811.html (analog-to-digital converter reference, as some timer chips include A/D).