Skip to main content
B
BTrem.1
Visitor II
September 5, 2020
Question

Using Segger J-tag on Nucleo-G431RB loss of Vt

  • September 5, 2020
  • 2 replies
  • 592 views

I want to do an experiment with the Nucleo-G431RB board on a jtag bus but I'm already seeing something strange. This board he has a built in ST-Link and also a jtag connector (CN4) for an external debugger. The manual says the external debugger can be used with the ST-Link disabled by putting a reset jumper on J1. But when I do this the the +3.3V to Vt goes to 0, even while I'm leaving the ST-Link USB cable still plugged in. This of course prevents the Segger j-link from connecting.

If I don't hold the ST-link in reset the Segger J-link does connect in jtag mode and does appear to work. However, I note in my Keil debugger the interface see's two devices, one the STMG431RB and the other unknown.

I eventually want to chain a 2nd Nucleo-G431 with this first one to see if I can individually control two G431's on a chained j-tag bus. Do I need to find a way to disable the ST-links? Why would a reset (conn J1) cause 3.3V to shut down.

In my final application the ST-Links won't be on the target boards.

Thanks,

    This topic has been closed for replies.

    2 replies

    B
    BTrem.1Author
    Visitor II
    September 8, 2020

    Adding some additional notes:

    This is in the UM2505 Manual on the G431 Nucleo board:

    0693W000003R6dAQAS.gif

    #1 does work but the j-tag see's two devices, the G431 and an "unknown"

    #2 does NOT work. With JP1 in place there is no +3.3V at CN4-3 (Vt).

    Is +3.3V at CN4-3 supplied from the SEGGER debugger, or is it just sampled? If sampled, where is +3.3V sourced from?

    My problem persists ... The J-LINK mini does not see the 2nd G431, only see's the first in the chain.

    Can anyone offer advice on what to pursue next? I'm stuck ....

    B
    BTrem.1Author
    Visitor II
    September 15, 2020

    Answering my own question,

    With the JP1 reset jumper in place I don't think the +3.3 supply gets the enable signal from the ST-LINK MCU.

    I changed the JP5 jumper to +5V_CHRGR and left JP1 with the reset. Now both MCU's power up. The J-Tag still only recognizes one MCU however. As a note the J-Tag see's two devices in that MCU which I understand is the M4 core and the FPU. So chaining two G431 MCU's should result in seeing 4 J-Tag devices.

    Still trying to get it to see the 2nd MCU. Will report back when I get more info.

    Terms & ConditionsAccessibility statement