Pages created and updated by Terry Sturtevant Date Posted: March 28, 2018

CP480 Wireless Communication and Networks Laboratory

Universal Asynchronous Receiver Transmitter (UART)


This week's laboratory investigates RS-232 (or EIA 232) communication.


The RS-232 protocol has been around since 1962. Originally designed to basically connect a single "smart" device to a single "dumb" device, it is now still very commonly used to connect sensors to microprocessors or microcontrollers, and so will remain relevant for the forseable future. It's also one of the simplest serial protocols, and so it's easy to study. The Arduino board has a UART built-in, so it can be used to study RS-232 communications. Note: The UART pins on the Arduino will be at TTL levels, not at acceptable RS-232 levels.


  1. Become familiar with the hardware layer of UART.



  1. Connect the Arduino to the oscilloscope, using one channel for each of the TxD and RxD signals.
  2. Use SimpleSerialCharOut to repeatedly send a character out from the UART.
  3. Watch the signals on the scope and identify the transmission of a single character. Sketch the signal or print it.
  4. On the sketch, identify the start bit(s), stop bit(s), and the character bits to show how the character can be decoded from the signal. If you're not sure which end of the pattern is the beginning and which is the end, change the character being sent to clarify.
  5. On the sketch, show the time scale and explain how it relates to the baud rate. (i.e. Identify how the time for one bit is determined from the baud rate.)

  6. The built-in UART on the Arduino board is also used for USB communication with the board, so using it for other things can cause problems. There is a library for software serial ports which allows you to use other pins to create a UART. The SimpleSoftwareSerialCharOut example makes the changes to the previous example so that you can now change the pins to any not used by the shield using a software serial port.
    Load the software serial sketch and change the pins to demonstrate that ability.

  7. Combine this sketch with the lcd shield sketch so that pressing different buttons on the display shield will change the character being transmitted.
  8. Show your pin assignments on the diagram.
Demonstrate and explain your results to the lab instructor


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Wilfrid Laurier University