BOR in STM32U083

[KSzcz.2]

Hello,
I found some discrepancy in BOR configuration for STM32U083CCT6 processor between reference manual [1] and HAL implementation [2]. It concerns BOR_LEV[0:2] bits (bits 10:8) in FLASH_OPTR register. The RM [1] talks of four levels (000: 1.7 V, 001: 2.0 V, 010: 2.2 V, 011: 2.5 V, 100: 2.8 V), in HAL [2] bit 8 is used to enable BOR (OB_BOR_ENABLE in stm32u0xx_hal_flash.h, FLASH_OPTR_BOR_EN in stm32u083xx.h), and the next bits (the remaining two) are used to set the level, importantly, the RISING one (00: 2.1 V, 01: 2.3 V, 10: 2.6 V, 11: 2.9 V), and the next two bits (12:11, which are described in the RM as reserved) are used to set the reaction of the BOR circuit to the falling voltage (00: 2.0 V, 01: 2.2 V, 10: 2.5 V, 11: 2.8 V). So the implementation in HAL is wider (based on 5 bits) and seems more advanced than the one given in the RM. I will add that the erratum [3] is silent on this topic.

So, the question is which BOR settings in the STM32U083 processor are correct?

[1] RM0503, Rev 2 (26-Mar-2024), Reference manual, STM32U0 series advanced Arm®-based 32-bit MCUs
[2] STM32CubeU0 Firmware Package V1.2.0 / 30-October-2024
[3] ES0602, Rev 3 (February 2024), Errata sheet, STM32U073xx and STM32U083xx device errata

[KDJEM.1]

Hello @KSzcz.2 and welcome to the community;

First of all, thank you for posting.

You can find the correct BOR settings in the below:

This issue has already been reported internally to align reference manual, datasheet, STM32Cube_Fw_U0 and STM32CubeMX with this description.

Internal ticket number: 203504 (This is an internal tracking number and is not accessible or usable by customers)

Thank you.

Kaouthar

[KSzcz.2]

Thank you for your reply.

But what about bits 12:11? They are still assigned as reserved, but both in HAL and also in DS14463 - Rev 2 (18-Mar-2024) in 3.6.2 Power supply supervisor, can be read that "four (level as used) for falling VDD". A piece of stm32u083xx.h below:

[KDJEM.1 · Accepted solution]

Hello @KSzcz.2;

Bits 12:11 are reserved. As I mentioned in my last reply the datasheet, STM32Cube_Fw_U0 (stm32u083xx.h and stm32u0xx_hal_flash.h), and STM32CubeMx will be aligned with this description.

Thank you.

Kaouthar