POR RESET never work.

[kkim6]

Hi. I'm developing a custom wireless board using STM32WB09TEF7TR microcontroller.

Currently, my microcontroller doesn't reset when the VDD supply is turned on. (Power-on-reset, PORRSTF bit)

The microcontroller can only be reset by pulling-down the reset pin.

Is there any possible reason that causes this kind of behavior?

[TDK]

Why do you think it doesn't reset when VDD is applied?

[kkim6]

There are two pieces of evidence.

1. RCC -> CSR -> PORRSTF bit never becomes 1.

2. my coding is designed to start the BLE Advertisement when it is reset. and it doesn't start BLE when Vdd is turned on.

I'm using SMPS with a 10 uH inductor as the developer board did.

I'm investigating it because the previous circuit (STM32WB55VG6TR) used only 2.2 uH and there was no problem.

[STTwo-32]

Hello @kkim6 

Are you reading the PORRSTF bit by a direct reading of the RCC_CSR. If so, you will always have a 0. This register is mirrored at RAM location 0x20000010. In order to get actual register value user must read this RAM location. Direct register read always returns 0 (Note under the part 6.6.16 of the RM0505 Rev2).

Best Regards.

STTwo-32