In external RC mode, the oscillation signal is input to MCU internal through Xin, at this time, the state of Xout pin can be noted as the following two points:
1. When pin name is Xout/Fcpu, such as SN8P2700 series, Xout pin output Fcpu, and can not be used as general I/O port.
2. When pin name is Xout/Px.x, such as SN8P2500 series, Xout pin will automatically be released for general I/O port, the state can be set by the program, it can not output Fcpu or Fosc.