start bit

Asynchronous serial communication describes an asynchronous transmission protocol in which a start signal is sent prior to each byte, character or code word and a stop signal is sent after each code word. The start signal serves to prepare the receiving mechanism for the reception and registration of a symbol and the stop signal serves to bring the receiving mechanism to rest in preparation for the reception of the next symbol. A common kind of start-stop transmission is ASCII over RS-232, for example for use in teletypewriter operation.
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<protocol> A bit which signals the start of transmission of a character on a serial line. For an RS-423 signal, the line is normally at logical zero which there is no data and the start bit is a logical one. The zero-one transition tells the receiver when to start sampling the signal to extract the data bits.
[Is this upside-down?]
(1995-02-02)