Hello, I am facing a issue to generate generate a external clock from MCU on MCO1 GPIO pin on STM32F769I Discovery board.

[deepdarji]

Here are the details on MCO1 pin configurations,

 GPIO_InitStruct.Pin = LL_GPIO_PIN_8;

 GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;

 GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;

 GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;

 GPIO_InitStruct.Pull = LL_GPIO_PULL_NO;

 GPIO_InitStruct.Alternate = LL_GPIO_AF_0;

 LL_GPIO_Init(GPIOA, &GPIO_InitStruct);

Below is MCO1 clock configuration:

 LL_RCC_ConfigMCO(LL_RCC_MCO1SOURCE_HSE, LL_RCC_MCO1_DIV_5);

External HSE on STM32F769I-Disco board is of 25Mhz.

So expected signal on MCO1 (PA8) is smooth square wave with 5 MHz frequency.

but I am getting signal with variation in amplitude as shown in the attached Image file.

Please, do guide me if anything is missing in the configuration or attached waveform is expected and need to be handled outside for filtering a amplitude values.

Thank You,

Deep darji.

[Peter BENSCH · Accepted solution]

Welcome, @deepdarji​, to the community!

I am essentially seeing a square wave signal on your screenshot. Of course, depending on your connection to the oscilloscope, you have overshoots and undershoots on the edges, which are caused by inductive and capacitive effects of the cables. You can also see that very nicely in the Wikipedia article on overshoots explaining the reasons and basics behind.

Regards

/Peter

[deepdarji]

Thank you for the response.