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TMS320F28035 JTAG Pins and GPIO34 Reuse

Bhuvaneshwar kanade54447
Intellectual 680 points
Other Parts Discussed in Thread: TMS320F28035

Dear All,

         I want to design circuit using TMS320F28035 controller.

While assigning GPIO for different purpose i am stuck in allotting extra function to JTAG and GPIO34.

As mentioned in data sheets GPIO36 to GPIO38 are used for JTAG and debugging as well as GPIO34 will decide Boot Mode selection.

In normal configuration GPIO34 is kept pulled High.

         So can i use JTAG pins for other purpose like GPIO (input or Output) ? 

         Will it affect its operation ?

        GPIO34 can it be used with JTAG or Without JTAG as GPIO for other purpose like blink LED or taking Input , Will it affect its its Boot Mode Selection in stand Alone system ?

Thank You

Bhuvaneshwar Kanade

  • 0
    TI__Guru 57255 points

    Bhuvaneshwar,

    GPIO34: at startup the MCU will look at GPIO34 to help determine how to boot the device.  Therefore, if GPIO34 is being driven by an external device which is alive at the F28035's startup (for example a secondary chip's clock) you may have an issue.  After boot-up and your code begins running, GPIO34 may be used however you wish. 


    GPIO36-GPIO38: I would recommend using all other available IOs first.  However, if needed GPIOs 36-38 can be chosen via software to be GPIOs (as you mention).  Note that you will never be able to debug the device via JTAG (CCS) and use these pins as GPIOs at the exact same time.  Another interesting side effect is that if your code runs from FLASH and the code configures these pins as IOs, you should allow a way to go into a boot-mode other than boot-to-flash so that you can still reprogram the device via JTAG.  Much of this conversation is moot if you plan to use a serial port for debugging and/or use a serial port to program the device (although this is more difficult).

    Hopefully this helps.  Let us know if you have any other questions.


    Thank you,
    Brett