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page 36

8. INTERFACING COMPUTERS FOR DATA TRANSFER

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,

-1 or 2 stop bits

-Even, Odd, or No parity bit

-7 or 8 data bits

-1 start bit

 

data bits

stop bits

 

(7 or 8 bits high or low)

 

(1 or 2)

 

 

 

parity bit

 

start bit (low)

(a simple check

 

for data bits)

 

 

 

voltage (on data line)

tim

1 byte with overhead (a total of 10 or 11 bits)

Advantages,

-Very inexpensive

-Easy to hook up

-A popular communication port found on almost all computer hardware, regardless of age.