2.4 COM Port and Interrupt Settings
If your computer is equipped with one or more serial ports, you will need to change the COM Port setting on the modem (to either COM 3 or 4), or disable the PC's
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
Figure 2-3 Switch Block SW-1 Location
Table 2-1 Switch Block Settings
COM Port | IRQ | ||||||
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1 (3F8) | 4 | ON | ON | OFF | OFF | ON | OFF |
default |
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2 (2F8) | 3 | OFF | ON | OFF | ON | OFF | OFF |
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3 (3E8) | 5 | ON | OFF | OFF | OFF | OFF | ON |
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| 4* | ON | OFF | OFF | OFF | ON | OFF |
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4 (2E8) | 2(9)** | OFF | OFF | ON | OFF | OFF | OFF |
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| 3* | OFF | OFF | OFF | ON | OFF | OFF |
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*Use these IRQs only if your software can not address IRQ5 or IRQ2
**When using Windows with the modem set for IRQ2, select IRQ9 in Control Panel
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