STM32F072 Clock tree section shows how to select clock for USARTS 1-3, but not USART4. Were in the reference manual (RM0091 Rev 10) does it show how to select the clock source for USART4?

[DSudo.2]

The USART section states that all 4 USARTs can be clocked from a common set of 4 clock sources, but doesn't reference how to specify the clock for USART4 either.

[waclawek.jan · Accepted solution]

USART4 does not have a dedicated clock source switch in RCC_CFGR3, so that means that it runs always out of the APB clock (=PCLK).

Note, that RCC_CFGR3.USART3SW is available only for 'F091, so on 'F072 USART3 runs only out of the APB clock too.

JW

[DSudo.2]

Thanks so much for the quick answers, and the helpful hint about the USART3 clock source. I had missed that note about it only applying to F09x devices!