Strange Behaviors on PA0 Encoder Timer Input on NUCLEO H743ZI2

[Tanguy_GUERS]

Hello everyone,

I work on a demonstration product using a NUCLEO H743ZI2 board has a main board. 

I use two timer (TIM3 and TIM2) in encoder mode to measure the speed of two motors with precision.

But I didn't manage to get the theoretical results on 1 timer.

I checked the hardware to find a possible problem.

3 of the 4 GPIOs have no problems but on PA0 I found a sine signal with an amplitude of 3.3V and a frequency of 50MHz (the motors are not connected and the measurement is made directly on the GPIO).

So I tried to erase the software to see if it was a configuration problem but the problem persists on the microcontroller.

I don't understand where this signal can come from on the PA0 gpio.

I tried measuring PA0 on a new board with no software but I still found this signal at 50MHz, it is simply not at 3.3V but at 100mV.

Can you help me solve the problem please, is the gpio out of service, is the internal SRAM clock mapped on PA0?

[TDK]

Probably cross-talk from PA1.

Initialize it with a pullup/down or set it to an output value if you want to use it. Don't assign too much importance to the value on floating pins.

[Tanguy_GUERS]

I tried putting a pull down on PA0 and PA1 for TIM2 but to no avail the signal is still as strong on PA0.

Thank you for your answer, indeed it seems to be the correct answer. Is there a way to disable the RMII clock in software?

It does not come from the MCU but rather from the ethernet management device if I am not mistaken.