RTC configuration of outpot ALRM

[dToub.1]

Hello st community,

I work on stm32h7, and I use with RTC output alarmA, when the MCU power supple turned off, and RTC work with VBATT to wakeup some component with this signal, but this component needs any pules to wakeup and not woke up with first event ('0' to '1' or '1' to '0' )  he needs '0' to '1' and after this to go down '1' to '0' , so i have just the half way by config the alarm polarity to high,  but the SW not working yet to clear this signal, is there any way(some configuration of RTC output alarm) to auto clear RTC_SR_ALRAF flag for the output to go down without the SW?

[praiselittle · Accepted solution]

Hello, 

With H7 there is no way other than with SW. New microcontrollers like H5 or U5 can do it by setting the ALRxF
CLR (x = A or B) bits in RTC_CR . For your problem with H7, maybe you can use a LPTIM depending on your use case. 

Have a nice one !

[dToub.1]

Thanks a lot.

(That what i thought when i read RM-0455, but to make sure that i don't lost something, i posted this question) 

[Denys_T]

Hi, I am trying to get an alarm signal on pc13 pin but without success, could you give an example? I turn on alarm A (Routed to OUT), the interrupt occurs but nothing changes on the output.

[Denys_T]

It seems I found what was wrong, I carried out tests without turning off VDD and expected to see a signal on PC13 but nothing happened, but as soon as I turned off VDD the alarm signal appeared =))

[praiselittle]

Hello Denys_T, 

Firstly, may I ask if you are using a Nucleo board ?

If it's the case, I do think, it's normal cause PC13 is connected to the user button. You can remove SB51. You could  try it routed to the second output, PB2, but I do think you need to remove SB63.  

Also note the output are not available, if you don't use the alarm with the interruption, meaning it doesn't work in polling mode. 

Have a nice one, 

[praiselittle]

It's strange, I don't really understand this behavior. If I have some time, I will check it. 

[Denys_T]

Yes, if possible, I would like to sort this out completely.

[praiselittle]

Could you tell me if you are using a Nucleo board ? 

[Denys_T]

No, I'm using a homemade board with an STM32H750 processor