8.1 SERIAL DATA TRANSFER
A single communication line links two computers, and allows communications one bit at a time.
Typically strings are passed to and from a terminal, modem, mouse, etc.
Each string is broken up and each byte is sent one at a time.
Each byte is sent one bit at a time with the various framing options,
- Even, Odd, or No parity bit
Advantages,
- A popular communication port found on almost all computer hardware, regardless of age.
- Can be robust in an industrial environment
- Standards are very clearly defined
- can use common phone lines
Disadvantages,
Characteristics,
Speeds of 110, 150, 300, 600, 1200, 2400, 4800, 9600, 12000, 19200 baud (bits per second)
Can use as few as three wires for connection, or more as advanced handshaking lines are required.
Specialized chips, and modems are commercially available for using this interface
Popular standards are RS (Recommended Standard)-XXX published by the Electronics Industries Association
- RS-232 - available on almost all computers
- RS-422 - a popular industrial standard which can be noise resistant then RS-232
