2023-06-01 07:28 PM
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.
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2023-06-01 11:27 PM
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
2023-06-01 11:27 PM
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
2023-06-02 05:14 AM
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!