UART

Universal Asynchronous Receiver/Transmitter (UART), is one of the most simple communication interfaces for chip-to-chip communications. The protocol is asynchronous and uses no clock between the 2 devices, therefore, the 2 devices must operate at the same baud rate in order to communicate properly.

The interface uses 2 wires, a transmit (or Tx) and receive (or Rx), where the Tx of one chip is connected to the Rx of the other. UART transmissions are sent as packets, with 1 start bit, 5-9 data bits (most typically 8), an optional parity bit, and 1 or 2 stop bits. The parity bit allows the receiving UART to tell if any data has been corrupted during transmission.

Due to the relative simplicity of the protocol, the maximum baud rate or bandwidth is typically 115.2 kbps although speeds of up to 250 kbps are possible. It is a relatively simple hardware block and can be implemented mostly as a shift register with added start, stop and optionally parity bits. Due to the low speeds of a UART connection, it is typically used as a debug channel, to transmit text or simple command information.