From: email@example.com (Amy)
Subject: Re: Car speed conversion error
Date: 25 Nov 2002 07:37:09 -0800
References: <3DDB30C2.D6EC77EB@autometer.de> <firstname.lastname@example.org> <email@example.com> <3DDE3D5E.BA2F499E@xympatico.ca> <3DE053F7.2919CB9C@xympatico.ca>
NNTP-Posting-Date: 25 Nov 2002 15:37:09 GMT
> > Where CAN is available on the OBDII connector (diagnostics port) it will
> > often run at 50K or 500Kbps, and will often comply with the protocol
> > defined in 'keyword 2000'. I cannot remember if there is a mandatory PID
> > defined for ODO reading, but would not be surprised if there is.
> > It has been 6 months scince I had anything to do with implementing this
> > stuff, and I still wake up shaking, the specs are that badly written!
> I have got most of the relevant SAE and ISO OBD-II standards
> publications but, alas, none of them has an index. I am in the process
> of compiling one.
Suddenly, I really feel great knowing I am not the only one who find
the standards unclear, confusing, or incomplete...
The SAE standard I have for OBD II is SAE J1979. In sections 5.3 to
5.5 they have PID tables for various modes.
There is no mandatory PID for odometer reading.
I am not sure for the case of CAN protocol. But for J1850, they do
provide odometer information in three parameters:
- odometer - English, high resolution (1 bit = 1/8000 mile)
- odometer - English, low resolution (1 bit = 1/10 mile)
- odometer - metric, 1 bit = 1/64 km
The thing is I am not sure if all three parameters would be present on
the bus in most cars. I know mostly likely, a car in States would have
odometer reading in miles. But would it have both the high-resolution
or low-resolution parameters, I don't know. And in my project,
accuracy is a concern. I need to use parameter with high resolution,
whether it's odometer or vehicle speed.
As for CAN protocol, does anyone know which SAE or ISO standards I
need to find parameter definitions in terms of the parameter's
transmission rate, data length, PDU format, PDU specific, etc?
Thanks a lot!