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A2
SERIAL DATA COMMUNICATIONS
BACKGROUND
A2.1 INTRODUCTION TO SERIAL COMMUNICATION
Serial data communication is the most common means of transmitting
data from one point to another. In serial communication systems, the
data word or character is sent bit by bit over some kind of transmission
path. The receiving device recognizes each bit as they are received
and reassembles them back into the original data word. Serial data
communication systems are characterized by four primary factors:
1. Data speed or baud rate
2. Data format
3. Transmission medium
4. Clocking method
Serial data speed is referred to as Baud Rate. A baud is defined as a
signaling bit, which includes data bits as well as start/stop framing,
parity or any other bits that make up the data format. Typical
computer baud rates and their uses are:
110 - for old mechanical teletypes
300, 1200 - for low speed devices an older modems
9600 to 38400 baud for high speed devices and newer modems
Data format refers to the method or pattern the transmitter uses to send
the data word or character as a series of bits so that the receiver will
know how to recognize the pattern and reassemble the bits back into
the original data word. The most common method and the one used
in the 2303, is called asynchronous transmission because each character
is sent one at a time with an undetermined amount of time between
A-17
A2
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