Digital Dash Compatibility

[Terry/Carol Kelley]

The ECM will continuously output the dash stream as a message with some ID
(so the dash knows the stream is meant for it). It may take more than one
message. The message scheduler will rotate through a list of messages for
different modules and repeat this list. In between these messages, the ECM
listens for a "shut the hell up" command. When it gets this, it will pause
and wait for an ALDL request. Alternately, the ECM may just look for an ALDL
request (dump the diag list), halt the current message and output the ALDL
stream. I doubt seriously that the dash makes it's request this way and that
it is just listening to messages from the scheduler.

In the Vette it appears that the DIS stream is:

Number of cylinders
Accumulated fuel used
Accumulated distance

This doesn't contain the MPH and RPM so maybe the ECM ouputs the ALDL stream
alternately. It appears the Vette outputs the DIS in 160 baud mode, but can
be switched to 8192. Depending on the year of the dash, it may be 160 or
8192. This is were the work comes in.

Regards

Terry Kelley



-----Original Message-----
From: steve ravet <Steve.Ravet at arm.com>
To: gmecm at esl.eng.ohio-state.edu <gmecm at esl.eng.ohio-state.edu>
Date: Wednesday, March 24, 1999 12:21 PM
Subject: Re: Digital Dash Compatibility


>
>
>Gary Derian wrote:
>>
>> Fred, you may be in luck.  I think the digital dash for the '84-'89 Vette
is
>> self contained and uses conventional inputs from senders.  It is only the
>> newer stuff that has PCM driven clusters.  I have a prototype analog
>> instrument cluster that was built for the '84 Vette but never put into
>> production.  Its too bad the GM MBA-heads made the wrong decision on that
>> one.  The analog cluster is pretty nice, large speedo and tach with 6
round
>> dials arrayed 2 by 3 in between.  My point is this analog cluster is
>> completely conventional for its inputs, a sender and wire for each gauge.
>> It even uses the same connectors as the digital cluster and would be a
>> plug-in.
>
>As I recall from the service manual for my '89 vette the ALDL xmit line
>went to the dash as well as the ALDL connector.  The dash displayed
>instantaneous fuel economy which means it has to know injector
>pulsewidth, presumably it got that from listening the the ECM.  As far
>as the rest of the dash displays, don't know if they came from ALDL or
>dedicated sensors.  I was only interested in ALDL at the time.
>
>--steve
>
>ps I think I'm the only person in the world who liked the digital
>dash....
>
>>
>> Gary Derian <gderian at oh.verio.com>
>> >
>> > Frederic Breitwieser wrote:
>> > >
>> > > > digital dash), the dash communicated with the ECM over the ALDL
port
>> to
>> > > > get the information to display.  That means they have to run at the
>> same
>> > >
>> > > Interesting :)
>> > >
>> > > I had hoped that since the connectors fit, it would work
>> > > appropriately.  See, the analog cluster (minus the speedo)
>> > > from the Camaro worked on the older harness, so I was hoping
>> > > the digital dash piece was entirely self contained.
>> > >
>
>--
>Steve Ravet
>steve.ravet at arm.com
>Advanced Risc Machines, Inc.
>www.arm.com
>