HSE Bypass mode - Possible use of OSC_OUT as GPIO

[BPart.1]

Hi I am looking into using STM32F446RCTx for my design, which includes 2 x USB FS 2.0 (1 x Host + 1 x Device). Hence need to provide an external HSE. I want to use an Oscillator, meaning I setup the HSE as "Bypass Clock Source" .

With this setup I planned to use the pin 6 (PH1_OSC_OUT) as a GPIO for other functionalities. But the STM32CubeMX setting does not let me do this.

I see that this pin will be (OSC_OUT) High Impedance as per RM0390 - Page 120. Am I right in say that I MUST leave this pin NC and cannot free up to use as GPIO?

Thanks.

 

 

[mƎALLEm]

Hello,

I think that possibility is available only in newer products. STM32H7 can do that.

According to the STM32F446 reference manual. It says not. But I can check internally. Internal ticket number 220390 not accessible by the community members.

[BPart.1]

Hi Thanks for checking this out. 

[waclawek.jan]

> yes for STM32F446 you can use OSC_OUT and OSC32_OUT as GPIOs when HSE or LSE are in bypass mode

This is interesting. I've just tested and, yes, the 'F446 is different from the 'F427 (and thus presumably also 'F407) in this detail.

I've noticed another interesting and undocumented detail: in both the 'F446 and the 'F427, the RCC_CR.HSEBYP bit appears to be not reset by Software Reset, only by NRST and Power Reset.

JW

[Andrew Neil]

Similar question here:

How to set Hi-Z mode in PH1 (OSC_OUT) when using HSE BYPASS mode in STM32F446RE?