A Word About Com Ports And Irqs - US Robotics 002605-00 Manual

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A Word about COM Ports and
IRQs
Most computer accessories — a mouse,
sound card, enhanced graphics card, scanner,
etc. — require a special connection through
which they can communicate with the
computer. For an internal modem, it'scalled a
communications (COM) port. Most computers
have 1 or 2 COM ports but can have up to 4.
On an internal modem, the COM port is
represented by the modem itself.
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Each COM port uses an IRQ (interrupt
request). An accessory uses an IRQ to get the
attention of your computer's CPU (central
processing unit) so that the accessory can
perform a task. The computer stops what it's
doing, depending on the priority of the request,
to help the accessory perform its task. When
two accessories share an IRQ, it's like two
people asking different questions in unison to a
third person. Just as the person being asked the
two questions cannot understand either request,
a computer can lock up or otherwise fail to
communicate properly with your modem when
there is an IRQ conflict.
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