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An IRQ (interrupt request) is a signal generated by an
I/O device that notifies the computer of incoming data. Your
internal modem is capable of accessing IRQs 2, 3, 4, and 5.
I/O devices in your computer cannot share an IRQ with
another device at the same time. Since IRQs can not be
shared at the same time, COM 3 is generally configured to use
IRQ 5, and COM 4 to use IRQ 2. This avoids sharing of IRQs
with COM 1 (IRQ4) and COM 2 (IRQ3).
To change the default COM Port or IRQ settings from
COM 1/IRQ 4 to another setting, locate the Switch Block on
your internal modem (Figure 2-3). Refer to Table 2-1 to
configure the Switch Block to the COM Port and IRQ
combination needed for your application. Any time the
COM or IRQ setting for the modem is changed, the
settings in the software must be changed to match.
COM Port IRQ SW1-1 SW1-2 SW1-3 SW1-4 SW1-5 SW1-6
1 (3F8)
default
4 ON ON OFF OFF ON OFF
2 (2F8) 3 OFF ON OFF ON OFF OFF
3 (3E8) 5 ON OFF OFF OFF OFF ON
4* ON OFF OFF OFF ON OFF
4 (2E8) 2(9)** OFF OFF ON OFF OFF OFF
3* OFF OFF OFF ON OFF OFF
* Use these IRQs only if your software can not address IRQ 5 or IRQ 2
** When using Windows with the modem set for IRQ2, select IRQ9 in
Control Panel
SW1
Figure 2-3 Switch Block SW1 Location
Table 2-1 SW1 Settings