What FD, FE and FF hex values of chars represent in UART communication? For some time my UART won't work, and always returning me those three?
They often mean that communications do not work properly. The very first bit (the start bit) appears, but the data bits do not. Common reasons for that are:
- Bad connection in ground or data line (high resistance or capacitance)
- Sender's baudrate is way too high (sender sends at 57600, receiver listens at 9600)
- Sender's voltage is too low (1.8V sender sends data to 5.0V receiver)
- Power supply problems (regulator is overloaded or oscillating because capacitors are not big enough)
Nothing, they're just bytes. Why your device produces them and how your terminal emulator interprets them is implementation-specific, but they don't mean anything in a general sense.