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3. HARDWARE SETUP
3.7.2 Assigning IRQs for Expansion Cards
This is applicable only when MPS 1.4 Support is Disabled in section 4.6 Boot Menu.
Some expansion cards need an IRQ to operate. Generally, an IRQ must be exclu-
sively 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 moth-
erboard 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 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.
The following table lists the default IRQ assignments for standard PC devices. Use
this table when configuring your system and for resolving IRQ conflicts.
ISA Interrupt (IRQ) Assignments
ISA INT
Priority
ISA 00
1
ISA 01
2
ISA 02
N/A
ISA 03*
11
ISA 04*
12
ISA 05*
13
ISA 06
14
ISA 07*
15
ISA 08
3
ISA 09*
4
ISA 10*
5
ISA 11*
6
ISA 12*
7
ISA 13
8
ISA 14*
9
ISA 15*
10
*These IRQs are usually available for PCI devices.
PCI Interrupt (IRQ) Assignments
PCI Slot
PCI INTA PCI INTB PCI INTC PCI INTD
1 (32-bit)
PCI 00
2 (32-bit)
PCI 01
3 (32-bit)
PCI 02
4 (32-bit)
PCI 03
5 (64-bit)
PCI 05
6 (64-bit)
PCI 06
7 (32-bit)
PCI 07
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
PCI 10
PCI 11
PCI 12
PCI 10
PCI 11
PCI 12
PCI 13
PCI 14
PCI 15
PCI 13
PCI 14
PCI 15
PCI 13
PCI 14
User's Manual
PCI 12
PCI 11
PCI 10
PCI 15
PCI 14
PCI 13
PCI 15
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