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TRST on TMS570

Richard Burke
Expert 1910 points

Hello Forum,

This question relates to previous posts including http://e2e.ti.com/support/microcontrollers/hercules/f/312/t/155725.aspx.

We have experienced problems with power on reset on our own PCB. We experienced unreliable power on reset operation with TRST pulled high and solved the problem by pulling TRST low via a resistor. There seems to be confliciting information on the web about what to do with this pin and I have seen previous posts recommending that the pin be pulled high, low or left floating depending upon the JTAG interface being used.

Can somebody please clarify the recommended way to connect this pin?

Thanks,

Richard

  • 0
    TI__Guru**** 200206 points

    Hi Richard,

    The TRST should be at LOW during the power up.

    So if you use an emulator which doesn't have internal pull-up and pull-down (for example, XDS510 Plus), it is ok to leave the TRST floating (MCU has internal pull-down) or pull-down the TRST.

    If your emulator has internal pull-up (for example JLINK), we recommend a extra circuitry to pull the TRST low during power on, otherwise you should power on the board first them plug the emulator. 

    The RevB silicon will remove this feature. You can use either pull-up or pull-down for TRST. 

    Regards,

    QJ

  • 0 in reply to QJ Wang
    Expert 1910 points

    Hi QJ,

    Thanks for that. Our experience was that power on reset did not work reliably until we put an external pull-down on TRST. As it happens we use XDS510 Plus JTAG boxes and have had no problems using these.

    Could you clarify your comment about Rev B silicon? Are you saying that TRST will not affect power on reset?

    Regards,

    Richard

  • 0 in reply to Richard Burke
    TI__Guru**** 200206 points

    Hi Richard,

    The TRST itself should be affect the power-on-reset. If the TRST is at HIGH during the power up, you may see unexpected issues: JTAG cannot be connected, or Cannot load the program to flash correctly, or cannot execute the loaded code in flash/RAM. The RevB is not available right now. It has an extra circuitry to ensure TRST at LOW during power-up.

    Regards,

    QJ

  • 0 in reply to QJ Wang
    Expert 1910 points

    Hi QJ,

    The problems we encountered were not related to debugging but to running start-up code correctly (i.e. occasionally, the software did not run following a power on reset).

    Regards,

    Richard