Archive for July, 2007

CAN Bus In-Vehicle SAE J1979

July 18, 2007
Been working on vehicular CAN Bus of late.
In particular I have been investiagting SAE J1979 Diagnostic messaging.
With this you can query a vehicle for a range of parameters and states.
 
Besides emission control information you can get information on things like:
– Revs
– Speed
– How long the ignition has been on
– VIN #
– Battery Voltage
 
This is standardised query response mechanism that all vehicle s (US)have had to implement in US post 1997 (ODBII)
As of next year all new vehicles have to implement it on the CAN Bus.
The May 2007 SAE J1979 is a comprehensive list of of services and messages.
 
This avoids needing to obtain proprietary information that vehicle manufacturers are loathe to divulge.
There is though a lot of other information flying around of the CAN Bus that is not available through SAE J1979.
eg Battery state of charge.
 
Yesterday I got it all to work, including the multiframe messages required by some of responses such as VIN number.
I found an ISO/PAS document which explains the purpose of functional and physical addressing for the queries.
 
One could in principle develop a comprehensive diagnostic tool using J1979
 
With functional addressing you send a message to an address and all ECUS on the system respond with their physical address.
I got two responses on the vehicle I was using.  One is the the ECM the other was probably the TCM
 
Whilst these documents are public standards that actually cost a fair amount to purchase, especially if you need to purchase a few.

.NET Micro Framework Book

July 18, 2007
Got my copy of "Embedded Programming with the Microsoft .NET Micro Framework" from Amazon today.
This is a just released book, hot off the press.  I ordered it before it was finally published.
 
 
The book is quite readable and looks to be comprehensive and topical.