How can I implement Modbus rtu in STM32F0 discovery board?

[AvaTar]

You can start with searching for threads here, dealing with the very same topic.

[Pavel A.]

https://github.com/eziya/STM32_HAL_FREEMODBUS_RTU

https://github.com/MahdiKarimian/STM32-Modbus-SerialDMA

[AGold.1]

I have written a book on Modbus slave design using C targeted to STM32: https://www.amazon.com/dp/B086PNZF4W