Identifying BOR (Brown-Out Reset) Specifically in STM32G0 Series

[Anagha_Sasindran]

I am working on a project with the STM32G0 series microcontroller. There is a requirement in my project to identify a BOR (Brown-Out Reset) independently. In the previous version of the project, we used the STM32L4 series, where there is a reset flag bit (BORRSTF) in the RCC_CSR register to specifically identify the occurrence of a BOR.

In the STM32G0 series, there is a reset flag bit (PWRRSTF) available in the RCC_CSR register to indicate a power-related reset, which can be due to a BOR, POR (Power-On Reset), or PDR (Power-Down Reset). However, there is no dedicated reset flag for identifying a BOR alone.

Is there any other method available in the STM32G0 series to specifically identify a BOR?

[KDJEM.1]

Hello @Anagha_Sasindran ,

The BOR can be enabled or disabled only through option bytes. It is not available in Shutdown mode.

When the BOR is enabled, four BOR levels can be selected through option bytes, with independent configuration
for rising and falling thresholds. For more information about brown-out reset I advise you to take a look at AN5096 application note precisely section 1.2.1 Power-on reset (POR) / power-down reset (PDR) / brown-out reset (BOR)

Does my reply answer your request?

Thank you.

Kaouthar

[Anagha_Sasindran]

Hello Kaouthar,

Does this mean that since BOR is not available in shutdown mode, there is no need to check for BOR after wakeup?

[KDJEM.1]

Hello @Anagha_Sasindran,

Power and brown-out reset set all registers to their reset values except the registers of the RTC domain.

- When exiting Standby mode, all registers in the VCORE domain are set to their reset value.
Registers outside the VCORE domain (RTC, WKUP, IWDG, and Standby/Shutdown mode control) are not
impacted.

- When exiting Shutdown mode, the brown-out reset is generated, resetting all registers except those in the RTC
domain.

Thank you.

Kaouthar

[Anagha_Sasindran]

Hi Kaouthar,

I wanted to clarify whether a Brown-Out Reset (BOR) is available during shutdown mode in the STM32G0 series and how to differentiate between a Power-On Reset (POR) and a BOR, as both share the same flag bit (PWRRSTF bit of the RCC_CSR register).

I came across a response in the link below where it was mentioned that BOR itself is not available during shutdown mode. Instead, a POR occurs when exiting shutdown, and in the next version of the document, the reference to BOR will be replaced with POR.

Reset Behavior When Exiting SHUTDOWN Mode in STM32G0 Series

Could you please confirm if my understanding is correct? Since BOR is not applicable in shutdown mode, I can safely assume that whenever the MCU exits shutdown, the PWRRSTF bit being set always indicates a POR and not a BOR. This means I do not need to handle or differentiate BOR in this case, correct?

Thanks

Anagha

[KDJEM.1 · Accepted solution]

Hello @Anagha_Sasindran,

I confirm your understanding. 

The BOR isn’t available in the shutdown mode.  When exiting shutdown,  "brown-out reset" will be replaced by "power-on reset".

There’s no dedicated flag for BOR on STM32G0.

Thank you.

Kaouthar

[Anagha_Sasindran]

Hi Kaouthar,

Thank you so much for your response.

Thanks

Anagha