I have PCB made for STM32F103C8F46 with the attached schematic. At first I use ST-LINKV2 debugger to connect to the target. It connects successfully and able to flash the code as well. and it works well. But after some-time (like 5-10minutes) of keeping poweredon, voltage at the NRST pin of micro gets pulled to low and some short amplitude random pulses are seen at pin if I put scope.

Once I see NRST getting pulled low, then no-matter what I do it doesnot go back to normal. I replaced controller on the PCB and tried . But same behaviour again, first it works properly and then NRST held low. I had another blank PCB where I only put controller+debug bergsticks and tried connecting. This time I didn't even flash my code, just kept it powered on . Same behaviour occurred.

so totally I wasted 5 controllers debigging this.

When irrecgular behaviour occurred, I tried to load bootloader of STM using Boot0 held high. It sometimes gets connected and sometimes doesnot. When gets connected, I am able to flash hex. But after resetting Boot0 to low and running program, it resets back again. Really can't say whats happening.

So conclusion is either my schematic or PCB hardware has some fault. So please go through my schematic and point out mistakes if any.

 

Update: I know that NRST does not need a pull-up resistor and needs a 100nF capacitor. So I have tried this as-well. I am aware of the following schematic .

 

Sounds like the WDT to me. Have you disabled it?

Bon

 

Yes. I have tried it on fresh mcu - optionbytes 00FF5AA5 00FF00FF 00FF00FF 00FF00FF

 

Is your circuit controlling a motor?

 

Yes. Its supposed to control stepper motor. But right now I have not assembled its relevant components on-board. I just soldered micro+debug pins + crystal circuit.

 

Maybe not a very likely source of your trouble but how are you powering it?

 

Maybe not a very likely source of your trouble but how are you powering it?

Powered using ST-LINK V2 debigger itself. (J2 connection in circuit diagram)

Also please note that I can still sometimes connect to the chip by using HotplugMode, but I cannot flash it.

 

I have only one more thought on this, unfortunately. Where did you source the MCUs?

 

Where did you source the MCUs?

I assume, you are asking this to see if the mcu is fake...? I had it purchased from un-official dealer here in Bangalore, who usually provides original materials in past. Still, to be sure, I purchased same controller from another local dealer. But in both cases behaviour was same. Official dealers told "out of stock" so I can't help it.

On chip, text written clearly as STM32 F103C8T6

 

Might I suggest running my 'bluepill-diags-v1.6' ? It's GPL3 licensed and Freely available at
https://mecrisp-stellaris-folkdoc.sourceforge.io/bluepill-diags-v1.640.html

Abstract

The very popular Blue Pill Board has suffered at the hands of unscrupulous factories which supply cheaper Chinese clones instead of the original STM32F103C8T6 microprocessor. The replacement microprocessor usually has the Chinese FAB markings removed and fraudulently replaced with the STMicro part number and logo.

Bluepill Diagnostics attempts to discover the make and model of microprocessor installed in a Blue Pill Board, regardless of chip model number markings.
It does this via a simple user menu accessed via a USB serial terminal running on any PC and OS.

Cheers,
Terry