Chrysler vehicle LAN

[Ed Lansinger]

Bill Lewis wanted to know what the deal was with the in-car network
Chrysler uses in its minivan for communications between controllers.

I can't say for sure, but I'll bet it's the Chrysler "C-squared D"
system.  C^2D stands for "Chrysler Collision Detection" or something
else I can't remember.  What it is is your basic Carrier Sense
Multiple Access with Collision Detection (CSMA/CD) protocol.  It
runs out of a normal serial port (i.e. serial, asynchronous XMT/RCV
lines from the processor, not a full RS-232 serial port) with a glue
chip developed by Chrysler that handles the hardware interface.  The
full C^2D spec defines the hardware level (using this special chip
which I'm sure could be duplicated with discrete componenets by your
typical DIYer), the baud rate, and the communications protocol,
including headers, ID numbering for different types of nodes,
checksums, and back-off algorithm.

Basically (and my memory here is bound to be off), everything on the
net is sitting around waiting for a character to appear at its serial
port.  All RCV lines are listening to the one communication bus line
(through the glue chip).  All XMT lines are also tied to the same
line, but they are open-collector or something through the glue chip
so they don't affect it unless they are trying to transmit.  Anyone
who sends a message can verify that it was sent properly by watching
it come in through its own RCV line and checking the checksum.  You
could certainly do a master/slave protocol with this, but I recall
the intent was to let anyone talk at any time.

Fortunately, Chrysler wrote a nice SAE paper describing the system in
detail.  Sure wish I could remember the paper number.

The C^2D network first appeared on the C-body (Dynasty), as I recall.

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Ed Lansinger
General Motors Powertrain
Powertrain Control Center
Premium V Software & Calibration Group
Milford Proving Ground, Milford, MI
elansi01 at mpg.gmpt.gmeds.com  8-341-3049  (810) 684-3049
The pancakes stated above are mine, not my employer's.
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