Series resistors calculations for any interfaces

[Jonah9Veh]

Can someone please help with how to calculate the series current limiting resistors to be connected from STM32H7 or any MCU to transceivers or any other interfaces? Is there a general thumb rule followed? Also how to calculate the wattage of resistors in these cases? For UART, CAN, SPI, etc.

[Techn]

Ohms rule!!. You need to put the lost value of resistor based on the max current  given in the datasheet. For the worst case analysis one side will be at vcc and the other side will be at zero voltage, so we can approximate as VCC/max pin current. Wattage is i*i*R or i*V.