[Diy_efi] J1850 PWM Info Request

[steve ravet]

Rick Richard wrote:
> 
> I know someone on this list as either the SAE J1850 standard or the SAE
> HS-3000 book.  I'd like to implement the J1850 PWM protocol that Ford uses,
> but I can't find the protocol specs online, the books are expensive, and the
> custom chips are closed-source.

There are several layers to the protocol.  There is some info on the
gmecm page that I've collected, diy-efi.org, click gmecm, click ECM
info, click OBD2.  The device IDs, request numbers, etc. that are
specified in J2178 and J2190 are the same for all manufacturers,
although the good stuff is implemented in the "manufacturer defined"
sections.

The electrical portion of the protocol, which you're probably interested
in, is in a different document that I don't have a copy of.  I'm not
even sure which J document describes ford.  But, I've found plenty of
data sheets from motorola and intel that describe the GM format (J1850)
and basically contain all the info in J1850.  It seems like
semiconductor manufacturers that sell Ford interface chips would also
have similar data available in their datasheets.  It's taken me a couple
months of searching and reading to understand what specs apply to what,
and to locate stuff on the internet.  If you're just getting started
then keep looking, it's probably there but you have to learn how to find
it.

Like someone else mentioned, www.elmelectronics.com has a PWM <-> RS232
converter chip (it's a programmed PIC) that may work for you.

--steve

-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com

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