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Файл:(EOD).Computer hardware.pdf
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.