4 Attachment(s)
Eside input signal conditioning
I have looked through some of the input signals on the Eside and analyzed the circuit. I have made some assumptions... take care when using the information.
The signals in question are VATS, Traction control and MAF. There is a chip and a good number of resistors and capacitors involved with receiving each of these signals. This is done to control ESD, condition the signal against noise and provide hysteresis.
I have identified the chip to a functional level. It's pinout and function match that of LM339 quad comparitor. Comparitor chip is marked:
014
M66DB
89551
LM339 quad comparitor or a variant that shares the pin configuration.
This chip is used to provide a level switch at 2.5V instead of the standard vil/vih of the receiving part. A network of resistors provide hysteresis to avoid noise problems on the lines.
The outputs of these signals connect to a 68pin PLCC chip that has not been identified and is probably a custom chip for GM. In my notes I will name this part TPU for timer/processor unit.
Input:Output
VATS:TPU pin 20
Traction Contro:TPU pin 21
MAF:TPU pin 22
C1(RED) pin 26:TPU pin 23
The components to connect C1 26 are not installed on my board set. Unsure if/where it was used.
Here are some photos to indicate the components.
Attachment 13699
Attachment 13700
Attachment 13701
Attachment 13702
-Tom