I am attempting to pass data through my serial port and see the result. I have added myself to the group for /dev/ttyS0 and run

cat < /dev/ttyS0

on one terminal for reading of data. To write I tried

echo -e '123' > /dev/ttyS0

The commands don't throw any errors, but I don't see any output on the first terminal. Any ideas on what I'm doing wrong?


You are missing the loop-back connection/jumper. The serial port send data through pin 3 and receive them through pin 2.

As you are using same port, connect 2 ↔ 3 with a wire.

Reference: Wikipedia: Loopback

  • That may be an option I can try, but I was hoping that I can intercept the data or progmatically set it up to send to itself or another serial device without needing cables and such. Is this even possible? – MrJman006 Oct 16 '15 at 13:15
  • @MrJman006, No, that is not possible for real serial port (It has separate FIFO's for Input and Output with separate send & receive physical lines). Not the same as network interfaces, because port are logical and there is always virtual loopback interface setup by default (try: ifconfig -a, see lo) – user.dz Oct 16 '15 at 14:34

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