Stoppbiter

Stoppbiter are a component of asynchronous serial communication framing. They are the time intervals at the end of each transmitted character that keep the line in a defined state long enough for the receiver to recognize the end of the character and to prepare for the next one.

In typical UART and serial interfaces, a character is framed by a start bit, a set of data bits, an optional parity bit, and one or more stop bits. The start bit signals the beginning of a character, and the stop bits signal its end. The line is held in the idle state (usually high) during the stop bit(s). The duration of a stop bit is measured in bit times and depends on the configured baud rate.

Common configurations include one stop bit, two stop bits, and, in some older or specialized systems, one and a half stop bits. The choice of stop bit count affects reliability and throughput: too few stop bits can increase the risk of framing errors if timing is not exact, while too many stop bits reduce effective data throughput.

Stoppbiter are hardware-controlled and do not typically carry information themselves beyond signaling the end of a character. They interact with data bits and, if used, parity bits to form the complete asynchronous frame. In modern high-speed or synchronous protocols, framing may differ or be absent, but stoppbiter remain a fundamental concept in many legacy and embedded serial systems.