STM32 - USART - where is the REACK bit?

[Doug Barnes]

Posted on January 07, 2017 at 17:46

Hi,

Using the STMF746 DISCO board... looking at the example for USART6 - in the STM32-provided driver code, the software waits for USART.ISR[REACK] to become set.

The documentation shows the TEACK bit (bit 21 of the USART's ISR) but for the life of me, I cannot find REACK in RM0385 (October 2016).  It almost appears to be an undocumented bit.  From the software, it appears to be bit 22.

Can someone from ST please clarify the existence of this bit, and why it is in the software from ST but not in the reference manual.

(BTW, REACK is referenced in stm32f746xx.h and stm32f7xx_hal_uart.c and stm32f7xx_hal_usart.c)

Thanks.

#stm32f7 #usart #rs232 #serial #uart

[Imen.D]

Posted on January 10, 2017 at 09:32

Dear

firmwareguy

‌,

The REACK bit is used with the wakeup from stop feature.

In STM32F7, the USART doesn’t support the wakeup feature, so the REACK bit should not be documented.

I will report this issueinternally to

remove REACK bit from the HAL in the

coming versions.

Thanks for bringing this issue to our attention.

Best Regards

Imen

[Doug Barnes]

Posted on January 10, 2017 at 13:42

Thank you Imen, that is very helpful to know.

[David Annett]

This problem also appears to be present in the STM32F030 reference manual (RM0360) too. During debugging Atollic is showing that the REACK, TEACK and EOBF bits are set but the documentation does not mention them so I don't know if I should be worried about them. I am going to ignore them as I suspect that are not related to the bug I am chasing but I'm guessing either Atollic or RM0360 should be updated.