Voltage Drop from 3.3V to 1V on NRST Pin of STM32F070CBT6

Hi.

From schematic, not all four VDDs , three VSSs pins connected to power rails.(GND and +3V3A)

Also NRST pin is pulled up "strongly" while is already pulled up with 40Kohm Additionally is not connected in the same +3V3A rail but to the other side of MCU jumper.

In case a microAmmeter is connected to jumper, is possible to have this behavior.

"comes randomly in every 2 to 3 minutes" Is it possible to have an interference from GSM module?

Hi,

1. From schematic, not all four VDDs , three VSSs pins connected to power rails.(GND and +3V3A) - I don't understand, as per datasheet their are 5 VDDs and 4 GND in STM32F070CBT6.
2. Also NRST pin is pulled up "strongly" while is already pulled up with 40Kohm - I tried removing Pullup resistor but it does not make any changes.
3. Additionally is not connected in the same +3V3A rail but to the other side of MCU jumper - By shorting jumper with solder on PCB it connect +3V3A with VDD. Basically this jumper is placed to repairing purpose by splitting VDD of MCU from other components.
4. In case a microAmmeter is connected to jumper, is possible to have this behavior - Can you please explain this.
5. Is it possible to have an interference from GSM module? - I guess no. It makes no effect whether i switch off GSM or turn it OFF.

Hi

1. I observed from schematic the Vbat pin and PF6 and PF7 are not exist for this MCU. But the pin numbers are correct connected. So all VDD,VSS are ok.

NRST pin is also an output pin. it can be driven Low from an internal reset source. So check reset flags of clock controller's CSR register just after this described reset to find the reason of unexpected reset.