NRST Pin going low while programming for a milli second.

[Ragini]

Hii,

I am working with stm32f100 series microcontroller, where I am having issue with NRST pin, I have connected a capacitor of 0.1uF(also tried 10uF) between NRST pin and ground. Microcontroller has an internal pullup. and it is showing 3.3V at the terminal which is correct. but after connecting the programmer, when I am trying to load my program, there is a sudden fall in voltage at NRST(checked with oscilloscope) for just a millisecond. and this is disconnecting my board with the programmer. I am using STM32CubeProgrammer. how to resolve this.

I have not connected the WDG circuit to NRST.

The error I am getting , I have attached below.

[BarryWhit]

If the programmer can download and verify the downloaded code successfully, yet the connection is lost when your program starts running, there is something wrong with your program.

Double check that your program doesn't configure the SWD/NRST pins to perform another function.

[Ragini]

Thanks for your reply :smiling_face_with_smiling_eyes: 

I have already considered the fact that ,there can be issue with the code itself ,so I tried running that program on the other boards I have. It is working totally fine with them.

I also I tried different programs those are also not working with this board only ,and working fine with other boards .

Suggest me, what I can do now, any changes with the hardware or software ??

[BarryWhit]

1. Your CubeProgrammer log doesn't show verification being done. Can you turn it on, and post the results of verification?

2. Are you using an original ST-LINK or a clone? which signal, if any, did you connect to NRST?

3. Regardless of whether the debugger connection is lost, does the program itself appear to be running? can you get a simple led blinker program to download an run successfully?

4. Are you able to connect to the bootloader over UART and see if you get the same behavior that way?

Please go through all these checks and report back.

[Tesla DeLorean]

What kind of looped-back or external connectivity do you have?

Anything else attached to the NRST line? POR circuit? Another device?

Some chance the power supply is browning out?

Enough bulk capacitance on the supply/regulators?

Most likely a hardware issue on the board.

[Ragini · Accepted solution]

Thankyou for your replies :smiling_face_with_smiling_eyes:

I have solved the issue.

It was with the hardware.

Earlier I was not connecting NRST pin directly with the JTag/SWD connector. was just connecting the JTag connections.

Now I have connected the NRST pin using 0 ohm jumper resistor to the connector's NJTRST pin. and also I had to connect 10uF capacitor with NRST, 0.1uF was not working here.