7
Serial Communications
Introduction
There are a wide variety of serial communications protocols avail-
able, but all rely on some form of coding scheme to efficiently
and effectively transmit the serial data across the transmission
medium. In this chapter, not only will the common methods of
transmitting data be reviewed (RS-232 and Universal Serial Bus
(USB)), but in addition some useful coding mechanisms will be
described (Manchester, Code Mark Inversion, Non-Return-toZero –
NRZ, Non-Return-toZero-Inverted – NRZI) as they often are used
as part of a higher level transmission protocol. For example, the
NRZI coding technique is used in the USB protocol.
Manchester encoding and decoding
Manchester encoding is a simple coding scheme that translates
a basic ...