PIC24 spewing CAN messages even in reset

[billvon2]

I have a PIC24EP512GU810 and we are using both CAN bus interfaces for an application. We've been having trouble with spurious messages appearing on the CAN1 bus. They are always the same four messages, with ID's 521, 522, 523 and 524 hex. They are always six bytes long. They contain alternating data.

We've tried everything to stop them. I can even power down the board, ground MCLR with a jumper, then power the board back on - and they still appear. How can we be getting these when the PIC is in hardware reset? Is there a config bit or something that allows the CAN bus interface to always transmit, even in reset?

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[Ttelmah]

I'd be looking at how the lines driving the CAN transceivers are biased.
Understand that if the PIC is in reset, most of the lines are floating. Now
if the enable on the can transceiver can float into the active state, you
are then driving the bus. You need to ensure that when the PIC is not
driving the enable line, this by default is resistively pulled to the inactive
state.

[bryant@balancebitsconsult]

Good news I suppose. We're on the same team - it seems there was a random device that was publishing CAN messages on the same lines that the PIC was connected to.

Fun times.

PIC was fine all along.