User’s Manual
19
2-6. Assigning IRQs for Expansion Cards
Some expansion cards require an IRQ (Interrupt request vector) to operate.
Generally, each IRQ must be exclusively assigned to specific use. In a standard
design, there are 16 IRQ available with 11 of them already in used by other part of
the system.
Both ISA and PCI expansion cards may need to use IRQ. Cards installed in the ISA
Expansion Bus have the first priority to use the avail able system IRQs. Any
remaining IRQ then, may be assigned to this PCI Bus. Microsoft's Diagnostic
(MSD.EXE) utility included in the Windows directory can be used to see their map.
Make sure that there are no two devices using the same IRQ in the system.
Otherwise this will cause the system to hang up or give unexpected results. To
simplify the process, this motherboard complies with the Plug and Play (PnP)
specifications, which was developed to allow automatic system configuration.
Whenever a PnP-compliant card is added to the system, PnP cards and IRQs are
automatically assigned if available. If the system has both Legacy and PnP ISA
cards installed. IRQs are assigned to PnP cards from those not used by Legacy
cards. The PCI and PnP configuration in the BIOS setup utility can be used to
indicate which IRQs have being used by Legacy cards. For older Legacy cards that
do not work with the BIOS, you can contact your vendor for an ISA configuration
utility.
An IRQ number is automatically assigned to PCI expansion cards after those used
by Legacy and PnP ISA cards. In the PCI Bus design, the BIOS is automatically
assigned an IRQ to a PCI slot that has a card in it which requires an IRQ. To install
a PCI card, you need to set the correct "ADSEL" and "INT" (interrupt) assignment.
Please refer to "Chapter 2-5" Installing a Riser Card for detail assignments.
IRQ
Status Assignment
0
Used
Timer
1
Used
Keyboard
2
Used
Second 8259
3
Used
COM2
4
Used
COM1
5
Used
COM3
