UART

Universal Asynchronous Receiver-Transmitter (UART) is a serial communication protocol, usually used in embedded systems. It requires only two wires (plus a common ground). One wire transmits and the other wire receives. Each device controls their transmitter and reads from the receiver. Data is transmitted and received one bit at a time. Common baud rates are 115200 and 9600 bits per second.

Protocol

UART can be configured for different transmissions including parity bits, however the most common configuration is 8-bit frames with no parity. Additionally, data is always sent from least significant bit to most.

When no data is being sent, the line is pulled high. This is mostly historical, but it is a nice indicator that the connection is good.