cheap obd2 scanner

[Mike Turner/ENGR/HQ/KEMET/US]

I've started looking into doing the same thing. The company sent me off to
W2K driver school last year before money dried up and I had decided that a
windows driver using minimal hardware for aldl and vpw would be a fairly
unique thing to do. I started hacking the serial driver in the ddk but
after a few weeks decided that was a losing proposition. There is too much
baggage and overhead. Too much time was being spent getting around
"features" in the old code. Last week I started a clean sheet serial driver
to get the performance up and lose the junk ms built into the old serial
driver. A local board house (Sealevel Systems) makes various serial boards
and one of their programmers who used to work here told me they tweaked the
standard driver to support up to 4 channels simultaneously at 110k. When I
described what I was doing with the vpw, he agreed a clean sheet was about
the only way. Mine will be a filter driver placed just above the standard
one. An ioctl could turn on and off my driver's functions.

On the pic chip route, I've started working on a firewire (ieee1394)
attached version. At 400Mb/s, 1394 has the speed needed. My laptop came
with 1394 and I got several cards cheap from compgeeks. TI sampled me some
chips suitable for hubs and a couple for 1394 devices (non-hosts). I have
monitored a few generic obdii data streams and things are looking
promising. However, I have not got access to a dealer box to monitor yet.
I'm wondering if some of the proprietary things gm is doing is triggered by
"illegal" timing on the pulsed data that causes a mode change on the ecm.
IBM used to use that technique a lot.

If you hit any brick walls, let me know. Maybe we can compare notes.
Sometimes it's hard to see the data for the bits. :)





"Paul Blackmore" <paul at blacky.co.nz>@diy-efi.org on 08/30/2001 12:40:12 AM

Please respond to gmecm at diy-efi.org

Sent by:  owner-gmecm at diy-efi.org


To:   <sabatine at epix.net>
cc:   "Gmecm" <gmecm at diy-efi.org>
Subject:  Re: cheap obd2 scanner


Hi Len,

When I said I was having a few teething problems I was referring to getting
the
PC to react fast enough to "see" the VPW pulses - even at 10.4Kbs.

I don't think it will be possible to read 41.6Kbs but if I sort out the
10.4KBs,
I'll give it a go.

The clock I am using (on my pentium) is only about 1.2Mhz which means I can
probably see pulses at 20 micro seconds, with some accuracy - given the lag
of
servicing an interrupt (about 10us). At 41.6Kbs we're looking at pulses
about
20-50 micro seconds so it probably wouldn't be 100% accurate.

Or I could write the whole thing in assembler :-P

It'd be best left to a pic type circuit which is also in the works.

Cheers
Paul

Date: Wed, 29 Aug 2001 22:16:12 -0400
From: Len Sabatine <sabatine at epix.net>
Subject: Re: cheap obd2 scanner

     Paul , Make your virtual device driver switch to 41.6Kbs , You'll
become a
     Hero in short order. Then things become easier for folks to monitor
a  Flash
     programming session , or other in VPW  hi speed mode.
     In real terms , This isn't easily accomplished in software only , Good
Luck !!
     Len




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