10.4 & 41.6 Waveforms

Im trying to put together a scan tool using an mc68000p8 processor and some PICs. It will also have a UART for serial comms to a PC and an LCD used as stand alone. Im going to try and code the PIC's to emulate a VPW UART to the microprocessor. 10.4 Kbps i am 99% positive i can do. 41.6Kbps though i am at a loss. I cant find any specs on it, as i am resource limited :). From what i see it wont actually be 41.6 Kbps single wire VPW, but 2-wire PWM(i think like ford uses). Does anyone have specs on what the physical data stream GM uses for the 41.6Kbps mode is? Like a waveform or timing diagram. I think once i get the code working for 41.6K a cheap DIY scan tool/programmer will be easy for anyone to build and modify with the source code. Then you guys can change fuel tables till you puke. Anyway some help would be..well helpful, and greatly appreciated!
-Max

GM dosn't use the 2-wire 41.6kbps PWM protocol.
If you wanted to make a scanner for both GM and Ford
this page has some links to Oki Semiconductor's MSM6636 IC for Fords PWM format.

Some of the Packet structure info dosn't look right but it still has a lot of good info on timing requirments.

I'm guessing the 41.6Kbps mode is just the 4x mode GM uses. Which would still be on a single wire.
the links page has a PDF that shows the waveshaping and timing for the 10.4Kbps.

You would probably be able to just factor the 10.4Kbps timing by four for the 41.6Kbps. The timing requirments for J1850 aren't very tight since the auto environment is very noisy, which should make it easier for you.

I'm also just starting on some firmware for a programming interface cable using the PIC16F876. :) It's going to be for the Ford PWM protocol though.

Ok, just wanted some clarification, because i cant find anything on j1850 VPW @ 41.6kbps , just PWM.