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TM4C1294NCPDT: CAN bus status is going to fault when I short a ADC PIN to 3.3V

Priyadharshan Narendra Babu
Prodigy 10 points
Part Number: TM4C1294NCPDT

Hi, I am using PB0 and PB1 for CAN1 Rx and Tx. I can receive and send messages properly. Then I started initializing ADC pins. I am using 13 pins for ADC measurements. For testing I shorted one by one to 3.3V and ground I am seeing the respective adc values change to 4095 and 0 as it should. But wierdly, few ADC pins like PB5, PD6, PD0, etc, when I short to 3.3V or ground the entire CAN bus goes down. and these are the register values I am seeing.

I used similar validation procedure for GPIO pin validation, where I just short them to 3.3 and GND. They all worked fine.

  • 0
    TI__Guru**** 191486 points

    Hi,

      Are you running on the LaunchPad or your custom board? Can you repeat the same on the LaunchPad?

      You seem to be getting CAN errors but I don't know why. I can't think of a reason that the CAN will fail when you short pins like PB5 and etc to either GND or VDD unless you accidently short between the VDD and GND rails or there is some noise coupled to the CAN bus. 

      Why don't you probe the CAN bus and show scope cap on the moment when you short  PB5, PD6, PD0 to either GND or VDD. What do you see? Do the same for running on the launchPad as well as on your custom board. Compare the waveform between them. 

      What CAN transceiver do you have? Can you also check you have proper CAN bus termination resistance. 

  • 0 in reply to Charles Tsai
    Prodigy 10 points

    Hi Sorry for late reply. This only happened  while testing with launchpad-TM4C1294NCPDTT3. With the custom board design I tested and it was working fine. I will check the CAN waveform when I short the ADC pin PB5 to power and GND and send you a snapshot.

  • 0 in reply to Priyadharshan Narendra Babu
    TI__Guru**** 191486 points

    Hi,

      Please note that the LaunchPad does not have an integrated CAN transceiver on it. I'm not sure how you are testing the CAN transmission using the LaunchPad. I suppose you add a transceiver and the correct termination resistor, correct?