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SERIAL (RS232)
PORT TROUBLESHOOTING
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CONTENTS AT A GLANCE
Although the parallel port is slowly gaining acceptance as a peripheral communication
port, early PCs used the parallel port almost exclusively for local printers. As more and
more peripherals became available for the PC, alternative methods of communication
were required that were ill-suited for parallel connections at the time. The Electronics In-
Understanding Asynchronous
Communication
The data frame
Signal levels
Baud vs. bps
Understanding the Serial Port
Addresses and interrupts
DTE vs. DCE
Serial-Port Signals
TX and RX
RTS and CTS
DTR and DSR
DCD
RI
IrDA Port Issues
Installing the IrDA driver(s)
Removing the IrDA driver(s)
IrDA tips
Troubleshooting the Serial Port
Serial-port conflicts
Match the settings
Frame it right
Finding a port address with debug
General symptoms
Further Study
dustry Association (EIA) developed a standard for serial communication. Instead of send-
ing eight bits at a time over a set of data lines, only two data lines were used: one to trans-
mit data and one to receive data. The EIA denoted its serial standard as RS-232 (or simply
the serial port). A serial port offers several distinct advantages over early parallel ports.
First, the serial port was designed to be bi-directional, right from the start. This made se-
rial the preferred method for interactive devices, such as modems, mice, etc. Second, the
serial port used fewer physical signal lines than the parallel port. This made cabling less
expensive and reduced potential connector problems. Where a printer cable is generally
limited to two meters in length, a serial cable can easily exceed 60 meters. This difference
opened the way for basic local networking. This chapter shows you the essential concepts
of serial communication and port operation, then guides you through a series of trou-
bleshooting procedures.
Understanding Asynchronous
Communication
The serial port is not terribly difficult to grasp, but its operation is a bit more involved than
that