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2-5-2 Assigning IRQs For Expansion Card
Some expansion cards need to assign an IRQ address to operate. Generally speaking, an IRQ
address must exclusively assign to one use only. With standard factory design, there are 16 IRQs
available, but most of them are already in use.
Standard Interrupt Assignments
IRQ Priority Standard function
0 N/A System Timer
1 N/A Keyboard Controller
2 N/A Programmable Interrupt
3 * 8 Communications Port (COM2)
4 * 9 Communications Port (COM1)
5 * 6 Sound Card (sometimes LPT2)
6 * 11 Floppy Disk Controller
7 * 7 Printer Port (LPT1)
8 N/A System CMOS/Real Time Clock
9 * 10 ACPI Mode when enabled
10 * 3 IRQ Holder for PCI Steering
11 * 2 IRQ Holder for PCI Steering
12 * 4 PS/2 Compatible Mouse Port
13 N/A Numeric Data Processor
14 * 5 Primary IDE Channel
15 * 1 Secondary IDE Channel
* These IRQs are usually available for ISA or PCI devices.
2-5-3 Interrupt Request Table For This Motherboard
Interrupt requests are shared as shown the table below:
INT A INT B INT C INT D
PCI slot 1 Shared ⎯ ⎯ ⎯
PCI slot 2 ⎯ Shared ⎯ ⎯
PCI slot 3 ⎯ ⎯ Shared ⎯
PCI slot 4 ⎯ ⎯ ⎯ Shared
PCI slot 5 Shared ⎯ ⎯ ⎯
AGP slot Shared ⎯ ⎯ ⎯
AC97/MC97 ⎯ ⎯ Shared ⎯
Onboard USB ⎯ ⎯ ⎯ Shared
Onboard USB 1 ⎯ ⎯ ⎯ Shared
Onboard USB 2 ⎯ ⎯ ⎯ Shared
IMPORTANT! While using PCI cards on shared slots, make sure that the drivers support
“Shared IRQ” or that the cards don’t need IRQ assignments. Conflicts will
arise between the two PCI groups that will make the system unstable or
cards inoperable.