UART - Universal Asyncrohonus Transmitter Reciever

What is UART?

• UART is a protocol that is used to communicate between microcontrollers

• It is typically implemented with the following 3 physical logic levels:

  • TTL

  • RS-232

  • RS-422

  • RS-485

• For those who have used Arduino, UART is the protocol that is used to facilitate ‘Serial’ communication

Signals Overview

• TX

  • Transmit signal as viewed from a microcontroller (i.e. signals will be going out of this pin)

• RX

  • Receive signal as viewed from a microcontroller (i.e. signals will be coming into this pin)

• RTS

  • Request to send, either high or low

• CTS

  • Cleared to send data, either high or low

Note, the TX wires of one microcontroller are wired to the RX wires of the other microcontroller. A similar situation occurs on the RTS and CTS wires. Always verify that the TX and RX wires are swapped.

Theory of Operation

• Serial protocols can be characterized into 2 types, synchronous and asynchronous. As you may have guessed by the acronym, the asynchronous in UART refers to the fact that the protocol is asynchronous. It is outside the scope of this document to discuss the advantages and disadvantages of each type.