UART

A UART, or Universal Asynchronous Receiver-Transmitter, is a hardware peripheral used for serial communication. It converts parallel data to serial form for transmission and converts incoming serial data back to parallel form. It is asynchronous, meaning it does not require a separate clock signal; both ends agree on a baud rate and framing parameters beforehand.

Data is framed in a pattern that is widely used: a start bit (usually 0), followed by a number of data bits (commonly 8; 7 is also used), an optional parity bit for error detection, and one or more stop bits (1 or 2). Bits are transmitted least-significant-bit first. The baud rate determines bit timing; both sides must operate at the same baud rate to sample correctly.

Operation: The transmitter loads a data byte into a shift register and transmits it serially through the TX line. The receiver samples incoming bits using a baud-rate clock and reconstructs the byte, optionally checking parity and stop bits. Many UARTs support flow control via RTS/CTS or software XON/XOFF.

Electrical interfaces vary: microcontroller UARTs typically use TTL or CMOS level signals (0 to Vcc). For longer connections or standards compliance, level shifters and line drivers are used to support RS-232 voltage levels or RS-485 differential signaling.

Applications: UART is a common serial interface for microcontrollers, modules, and embedded devices, used to connect to PCs, GPS receivers, Bluetooth modules, sensors, and other microcontrollers. Some devices provide both UART and USART functionality; USARTs offer synchronous modes in addition to asynchronous operation.