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When I wrote the first edition of this book, the RS-232 serial port was the
workhorse of PC interfaces. Modems and scores of other peripherals connected
to PCs via the serial ports that were present on every machine.
When the Universal Serial Bus (USB) took hold in the late 1990s, many pre-
dicted that serial ports would soon be obsolete. Plenty of peripherals that for-
merly used the serial port have switched to USB. But some devices can’t use
USB or have requirements that USB alone can’t provide. Many embedded sys-
tems use serial ports because they’re inexpensive and less complex to program
compared to USB. Serial ports can use longer cables than USB allows. And the
RS-485 serial interface supports networks suitable for many monitoring and
control applications.
While most PCs no longer have built-in serial (COM) ports, the ports are easy
to add via USB converters. With converters, the number of expansion slots no
longer limits the number of serial ports a system can have. The SerialPort class
included in Microsoft’s .NET Framework shows that PC applications continue
to find COM-port communications useful.