3. HARDWARE 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. 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 inop- erable. The following table lists the default IRQ assignments for standard PC devices. Use this table when configuring your system and for resolving IRQ conflicts.
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 used 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 Expansion Cards 3. H/W SETUP *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 AGP Pro slot shared shared Onboard audio/AMR shared ASUS CUV4X-M User’s Manual 27