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Thread: Custom board with JTAG header for Teensy 3.2

  1. #1
    Junior Member
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    May 2015
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    Custom board with JTAG header for Teensy 3.2

    Hi,

    I want to design a Teensy 3.2 clone board with a JTAG header for debugging use, and would like to ask some advice.

    To support the normal bootloader, I will add this chip:
    https://www.pjrc.com/store/ic_mkl02.html

    I will use this board as a base:
    https://github.com/thewknd/teensy-bo...0board%20clone

    And add a JTAG header to the board with PTA3 to SWDIO and PTA0 to SWDCLK
    (as described here: https://mcuoneclipse.com/2014/08/09/...swd-debugging/)

    * How to disable the MKL04Z32 bootloader chip while debugging over JTAG?
    In the Teensy 3.2 reference schematic (https://www.pjrc.com/teensy/schematic32.gif) I see that PTA4 and PTA5 on the MKL04Z32 bootloader chip are tied together with RESET_B on the main chip. I will connect all these to the JTAG RESET pin. Is that enough to disable the MKL04Z32 bootloader while debugging over JTAG, or do I need something extra to disable the chip?

    * Suitable debugger
    Can somebody suggest a reasonably priced debugger to get? It needs to work with pyOCD on mac os.
    (I have several mbed FRDM boards, but if I understand that they are limited to only program the exact same processor)

    I am primarily using the teensy 3.2 board with the mbed core.

  2. #2
    Senior Member Constantin's Avatar
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    My suggestion would be a 2x4 pin header with jumpers that connect the mkl02 when you want it (with shunt jumpers) and which disconnect it when you do not. Your debugger pins are thus exposed for debugging as needed.

    IIRC, Paul has mentioned that he may program a disable pin feature on the mkl02 in the future. That would obviate the need for the big pin header I mentioned and could allow you to enable something like the tag-connect series of debugger wiring harnesss.

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