STM32U083RC RTC wakeup mcu from stop mode

[clin.12]

I have three questions regarding the STM32U083RC：

1.Why  is the reset value of EXTI_IMR1 register 0xFFF80000？The EXTI line 19-21 is configurable lines。

2.I encountered a problem: when I used the NUCLEO-U083RC demo program to PWR_STOP2_RTC, I found that when the bit28 of the EXTI_IMR1 register was configured to 0 or 1, the RTC could wake up the MCU from stop mode. Why is the function of EXTI_IMR1 register not working?

3.Why does RTC/TAMP describe combined with EXTI lines 19 & 21 in the Vector table?

[Sarra.S]

Hi @clin.12, 

The EXTI_IMR1 register on the STM32U083RC resets to 0xFFF80000 because, by default:

• Interrupt requests for lines 0-18 are masked (disabled)
• Lines 19-21 are unmasked (enabled)

This setup reflects that EXTI lines 19-21 are configurable and active for interrupts out of reset, as defined in the EXTI register specifications.