UARTUSART

UART and USART are serial communication peripherals used in microcontrollers and embedded systems. A UART, or universal asynchronous receiver-transmitter, provides asynchronous serial communication by converting parallel data into a serial bit stream and back, without a separate clock line. A USART, or universal synchronous/asynchronous receiver-transmitter, can operate as a UART in asynchronous mode and also supports synchronous operation using a shared clock line for higher efficiency.

In asynchronous mode, data frames typically consist of a start bit, a configurable number of data bits (commonly 8), an optional parity bit, and one or two stop bits. The communicating devices must agree on the baud rate, which is set via baud rate generation. In synchronous mode, a clock line (CK) accompanies the data, allowing the transmitter and receiver to sample data on clock edges; this mode can enable multi-bit frames and higher throughputs, but requires clock coordination.

Common implementations provide a single peripheral capable of both modes, with configurable word length, parity, stop bits, and sometimes 9-bit data support or multi-processor addressing. Interfaces often remain level-shifted to TTL/CMOS or require transceivers for RS-232 or RS-485 signaling.

Applications include microcontroller console interfaces, debugging ports, inter-device communication, and PC serial ports. Advantages include simplicity and relatively low pin count; limitations include overhead for asynchronous framing and, in synchronous mode, the need for a shared clock and more complex hardware.

See also: RS-232, RS-485, serial communication, SPI, I2C.