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XDS110 VTREF Pin

Akash Patel
Expert 6245 points
Other Parts Discussed in Thread: EK-TM4C1294XL, LAUNCHXL-CC2650, CC2650

Hi team,

We are looking to use the XDS110 with the Tiva Series MCUs. I have the EK-TM4C1294XL which has an ARM standard 10-pin JTAG connector on it. This connector wants 3.3V on pin 1. However, pin 1 on the XDS110 using the Cortex-M 10-pin adapter is VTREF. It looks like this does not supply 3.3V. What is the purpose of this pin?

Is there a way I can get 3.3V on pin 1 of my connector?

Regards,

Akash Patel

  • 0
    TI__Guru**** 171044 points

    Hi Akash,

    (sorry I missed your call)

    Akash Patel said:
    However, pin 1 on the XDS110 using the Cortex-M 10-pin adapter is VTREF. It looks like this does not supply 3.3V. What is the purpose of this pin?

    The description of the VTREF pin (or TVRef, or other names) is shown below:

    http://processors.wiki.ti.com/index.php/XDS_Target_Connection_Guide#TVRef

    Its purpose is for the JTAG debug probe to detect power on the target board, not to supply power to the board. In other words, it is a sense (input) pin from the JTAG Debug Probe perspective.

    Does that help?

    Cheers,

    Rafael 

  • 0 in reply to desouza
    TI__Expert 6245 points
    Hi Rafael,

    Thanks for providing that link to the Wiki article.

    It would be ideal to have the voltage being delivered from the debugger to pin 1 on the Launchpad debug connector. I am assuming this is not possible?

    Is this possible on other debuggers like the XDS100v2 or XDS200?

    Regards,
    Akash Patel
  • 0 in reply to Akash Patel
    TI__Guru**** 171044 points

    Akash,

    Akash Patel said:
    It would be ideal to have the voltage being delivered from the debugger to pin 1 on the Launchpad debug connector. I am assuming this is not possible?

    Is this possible on other debuggers like the XDS100v2 or XDS200?

    Not really. If you are using very low power and is desperate for power, it is possible to try and harvest power from one of the JTAG communications pins at the moment you try to connect, but that would be terribly unreliable.

    Older XDS510 ISA or parallel port JTAG debuggers used to supply power through this pin, but that hasn't been the standard for quite some time. 

    Regards,

    Rafael

  • 0 in reply to Akash Patel
    Guru 92251 points

    Akash Patel said:
    It would be ideal to have the voltage being delivered from the debugger to pin 1 on the Launchpad debug connector.

    It depends on the XDS110. The built-in XDS110 on a LAUNCHXL-CC2650 can supply 3.3V on pin 1 of the Launchpad debug connector, and I was able to use the XDS110 on a LAUNCHXL-CC2650 to power a EK-TM4C1294XL through the 10-pin debug connector.

    The jumpers on the LAUNCHXL-CC2650 was removed to isolate the CC2650, and the 10-pin debug out on the LAUNCHXL-CC2650 was then connected to the EK-TM4C1294XL debug in.

  • 0 in reply to Chester Gillon
    TI__Guru**** 171044 points

    Chester,

    Chester Gillon said:
    It depends on the XDS110. The built-in XDS110 on a LAUNCHXL-CC2650 can supply 3.3V on pin 1 of the Launchpad debug connector, and I was able to use the XDS110 on a LAUNCHXL-CC2650 to power a EK-TM4C1294XL through the 10-pin debug connector.

    Although in practice this certainly works, this is non-compliant as it may improperly power the target if it demands more than the USB standard can supply or if the target has a hard output pin tied to VTRef (where a clash of outputs will happen and the stronger will win).

    In my CC2650 Launchpad Rev 1.1 the pin 1 is tied to the XDS110 Vcc, but the schematics of Rev 1.3 and the newer CC2640R2 have a jumper that allows VTRef pin to be fully compliant. 

    All this becomes important when you are designing your board and intend to rely the universal JTAG implementation - the XDS110 (or XDS100, or XDS200, etc.) will not supply power through VTRef. 

    Regards,

    Rafael