Assigning Irqs For Expansion Cards; Standard Interrupt Assignments; Interrupt Request Table For This Motherboard - Asus P4B-LA User Manual

3. HARDWARE SETUP

3.7.2 Assigning IRQs for Expansion Cards

Some expansion cards need an IRQ to operate. Generally, an IRQ must be assigned
exclusively 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 the motherboard
has PCI audio onboard, an additional IRQ will be used. If the motherboard also has
MIDI enabled, another IRQ will be used, leaving 4 IRQs free.

Standard Interrupt Assignments

IRQ Priority
0 1
1 2
2 N/A
3* 11
4* 12
5* 13
6 14
7* 15
8 3
9* 4
10* 5
11* 6
12* 7
13 8
14* 9
15* 10
*These IRQs are usually available for ISA or PCI devices.

Interrupt Request Table for this Motherboard

Interrupt requests are shared as shown by the following table:
PCI slot 1
PCI slot 2
PCI slot 3
PCI slot 4
PCI slot 5
Onboard USB controller HC0 —
Onboard USB controller HC1 —
AGP
LAN
Onboard Audio
IMPORTANT:
If using PCI cards on shared slots, make sure that the drivers sup-
port "Share IRQ" or that the cards do not need IRQ assignments. Conflicts will arise
between the two PCI groups that will make the system unstable or cards inoperable.
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 enabled
IRQ Holder for PCI Steering
IRQ Holder for PCI Steering
PS/2 Compatible Mouse Port
Numeric Data Processor
Primary IDE Channel
Secondary IDE Channel
A B C
— — —
— — —
— — —
— — —
— — —
— —
— —
used — —
— — —
— — —
P4B-LA Quick Start Manual
D E F
— — shared —
— — — used
— — — —
— shared — —
— — shared —
used — — —
— — — —
— — — —
— shared — —
— — shared —
G H
—
—
shared
—
—
—
shared
—
—
—
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