cheap obd2 scanner

[Len Sabatine]

     Is the use of IEEE1394  to communicate with a Vehicle PC kin to
     Killing gnats with a sledge hammer ?  OBD2 protocol is kinda like
     a slug in comparison. I believe you're still going to need to do
     some xlat from Pc serial across the OBD2 Physical and Hardware Layers .
      It takes a dedicated chip  for this work . GM VPW is a deterministic 
system
      with many Nodes that require Arbitration of commands and responses.
      Work on IOCTL will be very handy indeed . [ and very necessary].
      What ever has been learned about the old 8192 Uart is out the window
      with J1850 VPW.
      Len

>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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