Filter
Top Products
22
USB SINGLE-PORT HUB (RS-422/485)
Appendix C. Asynchronous
Communications
Serial data communications implies that individual bits
of a character are transmitted consecutively to a receiver
that assembles the bits back into a character. Data rate,
error checking, handshaking, and character framing
(start/stop bits) are pre-defined and must correspond at
both the transmitting and receiving ends.
Asynchronous communications is the standard means of
serial data communication for PC compatibles and PS/2
computers. The original PC was equipped with a
communication or COM: port that was designed around
an 8250 Universal Asynchronous Receiver Transmitter
(UART). This device allows asynchronous serial data to
be transferred through a simple and straightforward
programming interface. Character boundaries for
asynchronous communications are defined by a starting
bit followed by a pre-defined number of data bits (5, 6,
7, or 8). The end of the character is defined by the
transmission of a pre-defined number of stop bits
(usually 1, 1.5, or 2). An extra bit used for error
detection is often appended before the stop bits.