I noticed that in the code for my vortec PCM that there are two consecutive addresses that look as though theyre being used as Rx and Tx FIFOs for the OBD-II serial transmissions. After looking on DIY-EFI.org, I found another good piece of information that almost slipped through the cracks:

http://www.diy-efi.org/gmecm/ecm_info/obd2/mc68hc58.pdf

The PDF goes over the operation of the chip as well as what timing events its expecting to see for J1850 VPW transmissions. Good info if your be tuning with the older VPW based OBD-II PCMs. Maybe even could be used to design some cheap interfaces for datalogging and flashing the PCMs.

The chip in question is present in the PCM that Im working on. The size of the chip as well as the funky looking blue 4 MHz ceramic resonator hooked to it give it away. Its visible in the picture below, right next to the MPU, chip #9.

 

yep, I recall someone on DIY that was building a J1850 to serial device, maybe Steve or Shannen. I haven't had much luck finding it lately.

 

There is a site with freeware and schematics to build an interface. Have no idea how it actually works, but it looks promising. http://obddiagnostics.com/

 

24x7

Intersil makes HIP7010 low level IC for direct interfacing to 68HC05 and 68HC11 Style SPI ports for PCM side of things.

http://www.intersil.com/data/fn/fn3644.pdf

Also an interesting read....

//RF

 

Yeah, the reference manuals for the DLCs are definately useful. Without the one for the moto DLC, there would be no way to figure out how the recieve/transmit routines work, especially considering that all the code in these PCMs 10's of thousands of lines of pure brute force.