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26 ASUS A7N266-E User’s Manual
3. HARDWARE SETUP
CPU Installation
3. H/W SETUP
3.7.2 Assigning IRQs for Expansion Cards
Some expansion cards need an IRQ to operate. Generally, an IRQ must be
exclusively assigned to one use. In a standard design, there are 16 IRQs
available but most of them are already in use, leaving 6 IRQs free for
expansion cards. If your motherboard has PCI audio onboard, an additional
IRQ will be used. If your motherboard also has MIDI enabled, another IRQ
will be used, leaving 4 IRQs free.
IMPORTANT: If using PCI cards on shared slots, make sure that the drivers
support “Share IRQ” or that the cards do not need IRQ assignments. Conflicts
arise between the two PCI groups that will make the system unstable or
cards inoperable.
The following table lists the default IRQ assignments for standard PC devices.
Use this table when configuring your system and for resolving IRQ conflicts.
Standard Interrupt Assignments
IRQ Priority Standard Function
0 1 System Timer
1 2 Keyboard Controller
2 N/A Programmable Interrupt
3* 11 Communications Port (COM2)
4* 12 Communications Port (COM1)
5* 13 Sound Card (sometimes LPT2)
6 14 Floppy Disk Controller
7* 15 Printer Port (LPT1)
8 3 System CMOS/Real Time Clock
9* 4 ACPI Mode when used
10* 5 IRQ Holder for PCI Steering
11* 6 IRQ Holder for PCI Steering
12* 7 PS/2 Compatible Mouse Port
13 8 Numeric Data Processor
14* 9 Primary IDE Channel
15* 10 Secondary IDE Channel
*These IRQs are usually available for ISA or PCI devices.