ST-Link can't connect to STM32H750VB

[Avid]

I'm working on a custom PCB with an STM32H750VB and the ST-link is unable to find the target in both CubeProgrammer and St-link Utility via SWD, below are screenshots of some of the error messages I received and our microcontroller schematic. I've probed all of the VBAT, VDDA, VDDA, and VREF+ and they are all at 3.3V. All of the grounds are connected and are at 0V. I've tested the ST-link with a nucleo board and was able to connect to and program it. I measured VCAP1 and VCAP2 and they were at 1.008V, matching the voltage same pins on our nucleo board. The only odd thing I found was that NRST is at 0V when the board is powered. It's not shorted to GND and has a measured resistance of 16 Mohm. Even though the MCU has internal pullup on NRST, I tried adding an external pullup 10k but was still unable to receive a connection.

 

Could there be an issue that my schematic is indicating? One possibility is that the chip could just be fried since the SWD connector pinout on the custom PCB was initially incorrect with the pins being mirrored. Haven't yet replaced our current microcontroller but we have a new one on order.  

 

 

 

 

[AScha.3]

>chip could just be fried since the SWD connector pinout on the custom PCB was initially incorrect with the pins being mirrored

So it was powered with +/- at wrong polarity ? Was there > 100 mA input or so ? Then you killed it.

Is it getting hot now ?

[Avid]

 

Yes, the ST-link V2 SWD connector was connected to our board with the wrong polarity. Here's the kicad compared to a breakout board version of the connector pinout. Would the current output be enough to kill the chip?   

 

 

 

[AScha.3]

>ST-link V2 SWD connector + >Would the current output be enough to kill the chip?

Which st-link ? the "stick" V2 type ? maybe 50:50 chance.

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about 1V on VCAP is ok. 

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Is st-link still ok ? check it with another board.

[Michal Dudka]

Check exactly the state of the RST pin. If it is not in the "input with internal pullup" state, check if it is caused by some external component or by MCU itself. Investigate further RST pin status. 

[Avid]

Update: I replaced the microcontroller on the board and am now able to connect to it and send code, though NRST is still held low for some reason. So yeah, the STM32 was likely fried from connecting SWD backwards previously.