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User’s Manual 21
3. HARDWARE SETUP
System Memory
3. H/W SETUP
3.7.2Assigning 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 Standard Function
ISA 00 1 System Timer
ISA 01 2 Keyboard Controller
ISA 02 N/A Programmable Interrupt
ISA 03* 11 Communications Port (COM2)
ISA 04* 12 Communications Port (COM1)
ISA 05* 13 Sound Card (sometimes LPT2)
ISA 06 14 Floppy Disk Controller
ISA 07* 15 Printer Port (LPT1)
ISA 08 3 System CMOS/Real Time Clock
ISA 09* 4 ACPI Mode when used
ISA 10* 5 IRQ Holder for PCI Steering
ISA 11* 6 IRQ Holder for PCI Steering
ISA 12* 7 PS/2 Compatible Mouse Port
ISA 13 8 Numeric Data Processor
ISA 14* 9 Primary IDE Channel
ISA 15* 10 Secondary IDE Channel
*These IRQs are usually available for PCI devices.
PCI Interrupt (IRQ) Assignments
PCI Slot PCI INTAPCI INTBPCI INTCPCI INTD
1 (32-bit) PCI 00 PCI 10 PCI 11 PCI 12
2 (32-bit) PCI 01 PCI 12 PCI 10 PCI 11
3 (32-bit) PCI 02 PCI 11 PCI 12 PCI 10
4 (32-bit) PCI 03 PCI 13 PCI 14 PCI 15
5 (64-bit) PCI 05 PCI 15 PCI 13 PCI 14
6 (64-bit) PCI 06 PCI 14 PCI 15 PCI 13
7 (32-bit) PCI 07 PCI 13 PCI 14 PCI 15