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PC Serial Ports
A-8
Given the scenario described in item (1) above (that is, a mouse on COM1, a
fax/modem card on COM2, and the PassageWay Service Provider on COM3),
you might buy a bus mouse and configure it to use, say, IRQ2 or IRQ5. This
would then permit you to move the PassageWay Service Provider onto COM1
(IRQ4), where it then could be used simultaneously with both the mouse and
the fax/modem.
Likely candidates for conversion from a serial interface to some other interface
include mice (which can be converted to bus mice) and serial printers (which
can be converted to an additional parallel printer port).
Workaround 3: If your serial port hardware permits you to select IRQs
other than the default ones (IRQ3 and IRQ4), make use of one or more
unused IRQs in your system to assign to each COM port a unique IRQ.
This solution is generally not possible for built-in serial ports since these are
usually "hard-wired" and cannot be changed. Although most add-on cards
containing serial ports permit you to change the IRQs assigned to them, many
cards do not let you select IRQs other than IRQ3 and IRQ4. For example, an
internal modem card generally has jumpers or switches that permit you to
administer the serial interface on the card to be COM1, COM2, COM3, or
COM4, but the I/O port addresses and IRQs associated with each of these
configurations are usually fixed to the settings in the table.
Fortunately, some serial port add-on cards do permit you to select IRQs other
than 3 or 4 (the additional choices are often IRQ2 and IRQ5). If your serial
port hardware provides this flexibility — and at least one of the IRQ numbers
available as an option is currently unused in your PC setup — you can solve
the IRQ conflict directly.