Asus X900-PI4 - Manual (Page 28)

28 ASUS P4T User’s Manual
3. HARDWARE SETUP
Expansion Cards
3. H/W SETUP
3.7.2 Assigning IRQs for Expansion Cards
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.
Standard Interrupt Assignments
IRQ Priority Standard Function
0 1 System Timer
1 2 Keyboard Controller
2 N/A Programmable Interrupt
3* 11 Communications Port (COM2)
4* 12 Communications Port (COM1)
5* 13 Sound Card (sometimes LPT2)
6 14 Floppy Disk Controller
7* 15 Printer Port (LPT1)
8 3 System CMOS/Real Time Clock
9* 4 ACPI Mode when enabled
10* 5 IRQ Holder for PCI Steering
11* 6 IRQ Holder for PCI Steering
12* 7 PS/2 Compatible Mouse Port
13 8 Numeric Data Processor
14* 9 Primary IDE Channel
15* 10 Secondary IDE Channel
*These IRQs are usually available for ISA or PCI devices.
Interrupt Request Table for this Motherboard
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 — — —
Onboard USB controller — — — shared
SMBus — shared — —
IMPORTANT: If using PCI cards on shared slots, make sure that the drivers
support “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.