16
2-7-2 Assigning IRQs For Expansion Card
Some expansion cards need an IRQ to operate. Generally, an IRQ must be
exclusively assigned. In a standard design, there are 16 IRQs available, but
most of them might already be 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.
2-7-3 Interrupt Request Table For This Motherboard
Interrupt requests are shared as shown in 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! If 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 and will make the system unstable or
cards inoperable.
