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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
Associate III

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.

1 ACCEPTED SOLUTION

Accepted Solutions

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

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2 REPLIES 2

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

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!