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2.6.2 Configuring an expansion card
Some expansion cards need an IRQ to operate. Generally, an IRQ must be
exclusively assigned to one function at a time. In a standard design
configuration, 16 IRQs are available but most are already in use. Normally,
6 IRQs are free for expansion cards. If themotherboard 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. Sometimes IRQs
are "shared" by more than one function; in this case, IRQ assignments are
swapped automatically or adjusted through the BIOS firmware.
IMPORTANT!
drivers support "Share IRQ" or that the cards do not need IRQ
assignments. Otherwise, conflicts will arise between the two PCI groups,
making the system unstable and the card inoperable.
Standard Interrupt Assignments
This table lists the standard IRQ assignments for most PC devices.
IRQ
0
1
2
3*
4*
5*
6
7*
8
9*
10*
11*
12*
13
14*
15*
*These IRQs are usually available for ISA or PCI devices.
16
When using PCI cards on shared slots, ensure that the
Priority
1
2
N/A
11
12
13
14
15
3
4
5
6
7
8
9
10
Standard Function
System Timer
Keyboard Controller
Programmable Interrupt
Communications Port (COM2)
Communications Port (COM1)
Sound Card (sometimes LPT2)
Floppy Disk Controller
Printer Port (LPT1)
System CMOS/Real Time Clock
ACPI Mode when used
IRQ Holder for PCI Steering
IRQ Holder for PCI Steering
PS/2 Compatible Mouse Port
Numeric Data Processor
Primary IDE Channel
Secondary IDE Channel
IRQ assignments for
this motherboard
Chapter 2: Hardware information
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