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

BTrem.1
Senior II

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,

2 REPLIES 2
BTrem.1
Senior II

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 ....

BTrem.1
Senior II

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.