1.1 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,

- 1 or 2 stop bits

- Even, Odd, or No parity bit

- 7 or 8 data bits

- 1 start bit

 

 

 

• Advantages,

- Very inexpensive

- Easy to hook up

- 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,

- Very slow

 

• 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

- RS-423

- RS-449

 

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