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TMS320F280049C: CAN bus B

Phil Gillaspy
Prodigy 210 points
Part Number: TMS320F280049C

I am working with the LaunchpadXL-F280049C.  I have CAN bus A fully working.  Now I want to get the CAN bus b working as well.  I have CAN bus B routed to GPIOs 16 (for TX) and 17 (for Rx) which are accessible at pins 15 (Tx) and 14 (Rx)  of J2.  The problem is that I see anomalous behavior on the pins at J2. 

First, on pin 15 (Tx) of J2 I see no pulses with just an Oscope connected to the pin 16. HOWEVER, if I connect my CAN bus sniffer to pin 16 and pin 15, voila I see pulses on the Oscope, BUT the pulses only go down to 1.3 volts from 3.3V and so the sniffer doesn't recognize the CAN message.

Secondly, if I connect a CAN bus transceiver IC (SN65hvd, same as used for CAN bus A on Launchpad) to pins 16 & 15 of J2, I see no pulses at the TX input to the transceiver, in other words, the same as when I had no sniffer connected.

What is going on here?  Has anyone had CAN bus B working with an external transceiver?

  • 0
    Prodigy 210 points

    This is now solved.  I had to put a 10K pullup resistor to 3.3V on the Tx GPIO. I also discovered that the SN65HVD CAN transceiver IC did not support higher data rates, but is limited to 100Khz maximum (there is a different version of the SN65HVD that does support 1MHz bit rate).