STM32F100RB: MCO and USART1_CK conflict on PA8

[skirn9]

Posted on July 11, 2012 at 15:30

Hello,

I am using an STM32F100RB and want to use the clock output MCO on GPIO PA8, so i have to set the GPIO to 'alternate function push-pull'. But I also want to use USART1 with TX on GPIO PA9 and RX on GPIO PA10. So far so good. But the clock output USART1_CK is also using GPIO PA8 when set to 'alternate function push-pull' and with USART1 set to enabled. I do not need the clock output of USART1, so I will disable it in USART1_CR2 via the CKEN bit. So can I us PA8 as MCO without having any conflict with USART1_CK, because it is switched to high-Z?

[ColdWeather]

Posted on July 11, 2012 at 16:06

Correct.

[Tesla DeLorean]

Posted on July 11, 2012 at 17:43

ST really doesn't document the internal wiring, it's probably much more likely an OR combination from the AF output peripherals, and two wires/paths for TIM1_CH1 (ie TIM1_CH1_OUT and TIM1_CH1_IN)

If you don't use USART1 in synchronous mode and don't use TIM1 CH1 in an output mode, you'll get your MCO output.

[skirn9]

Posted on July 12, 2012 at 07:44

Thank You for your quick help.

I won't use USART1_CK nor TIM1_CH1 on PA8, so I will give it a try.