@tlfong01 i think what i've done in minicom on raspi is a loopback, isn't it? i've sent the screenshoot above (connect the GPIO14 and 15 together)

@RyanFikri Yes, you did it for minicom， But I am not sure if you just followed the tutorial blindly. I would suggest to repeat your loopback using (1) RealTerm, and show me the screen capture, with input say "abc123", and output echoing the same thing. i show the screen capture in at least two of the posts I referred. So this is an assignment.