We've tested sending data. It's time to test receiving it. Except that there's no other device that can send us some data ... or is there?

Enter: loopbacks

You can send data to yourself! Not very useful in production but very useful for debugging.

Older board revision / external serial module

Connect the TXO and the RXI pins of the serial module together using a male to male jumper wire as shown above.

Now enter some text into minicom/PuTTY and observe. What happens?

You should see three things:

  • As before, the TX (red) LED blinks on each key press.
  • But now the RX (green) LED blinks on each key press as well! This indicates that the serial module is receiving some data; the one it just sent.
  • Finally, on the minicom/PuTTY console, you should see that what you type echoes back to the console.

Newer board revision

If you have a newer revision of the board you can set up a loopback by shorting the PC4 and PC5 pins using a female to female jumper wire, like you did for the SWO pin.

You should now be able to send data to yourself.

Now try to enter some text into minicom/PuTTY and observe.

NOTE: To rule out the possibility of the existing firmware doing weird things to the serial pins (PC4 and PC5) we recommend holding the reset button while you enter text into minicom/PuTTY.

If all is working you should see what you type echoed back to minicom/PuTTY console.

Now that you are familiar with sending and receiving data over serial port using minicom/PuTTY, let's make your microcontroller and your computer talk!