AW: MSCAN interface on 56f803

Started by Bende Georg May 28, 2003
Hello Rick,
Thanks for your kind answer. Changing setup works for me and I can read REC
register in any state. I also managed to have automatic baud rate detection by
simply monitoring this counter - but I'd like to reset it after the correct
baudrate has been detected. I know that after a while it would automatically
decrease, but if the target baudrate is very low, I am too close to the "error
passive" limit at the end of the detection process. So, is there any way
completely resetting the CAN interface or just the REC itself?

Thanks for any kind of help,
Georg Bende
Abteilung Elektronik
Dr. Fritz Faulhaber GmbH & Co KG
Daimlerstr. 23
71101 Schaich
Tel: +49 7031 638294
-----Ursprgliche Nachricht-----
Von: Corey, Rick [mailto:]
Gesendet: Dienstag, 27. Mai 2003 17:33
An: Bende Georg
Betreff: RE: [motoroladsp] MSCAN interface on 56f803


Get into Soft Reset (, 8.10.5 & 8.10.4), maybe going into Sleep mode
first. Then you can set up MSCAN in a new way.

Merely auto-detecting baud rate may not do everything you wish. If the Sender
is using a different bit timing setup than you are, perhaps the bit timings can
be different enough to interfere with communication (I don't know, I just use
the same bit timing setup on both sides. I have 56803 on both sides.

I've noticed something that may help you. If I set up two nodes with
mis-matched baud rates (and they are the only two nodes on the network),
whichever node first tries to send a packet goes into a forever-loop re-sending
that packet over and over, until it gets a clean ACK. However, if there are
more than two nodes, any two nodes that agree on the baud rate will terminate
the re-try process.

By the way - I never had any luck reading the "REC/TEC" registers. I think you
might have to go into Soft Reset, then read them, then go back active. I rely
on the error interrupts RWRNIF, TWRNIF, RERRIF etc.

Good luck!

-----Original Message-----
From: Bende Georg [mailto:]
Sent: Monday, May 26, 2003 8:33 AM
Subject: [motoroladsp] MSCAN interface on 56f803

I'm wondering if anyone met the following problem: I'd like to have a CAN
device with automatic baudrate configuration. In the MSCAN specs there's a
special "listen only" mode which eases this, but unfortunately the MSCAN
implementation of the 56f803 doesn't have this operation mode. Because of this I
thought an implementation with some minor CAN violation would be the solution,
with listening to the bus and if errors occur, then reset CAN and change
baudrate. (in CANOpen there are a limited number of fixed baudrates) But if I
once enable CAN, I'm not able to disable it since this bit is write once, and I
didn't find any solution for totally resetting the CAN interface, or just the
error counter. Could anyone please give me a clue how to solve the situation?

Best wishes:
Georg Bende
Abteilung Elektronik
Dr. Fritz Faulhaber GmbH & Co KG
Daimlerstr. 23
71101 Schaich
Tel: +49 7031 638294

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