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This chapter introduces formats and protocols used in asynchronous serial

communications including low-level data formats, encoding methods for

binary and text data, and protocols to ensure reliable data transfer.



 
 


A serial port output that functions as a transmitter, or driver, sends bits one at a

time to a serial-port input that functions as a receiver, typically on a different

computer. The cable between the computers typically has a dedicated data path

for each direction. Some serial interfaces have a single, shared data path for both

directions, with the transmitters taking turns.

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    5 

   



The serial communications described in this book use an asynchronous proto-

col. In an asynchronous protocol, the interface doesn’t include a clock line.

Instead, each computer provides its own clock to use as a timing reference. The

computers must agree on a clock frequency, and the actual frequencies at each