| Channel | Assignment |
|---|---|
| DRQ 0 ( 8-bit) | User Available (Business audio) |
| DRQ 1 ( 8-bit) | User Available (Business audio or LAN) |
| DRQ 2 ( 8-bit) | DISKETTE DRIVE |
| DRQ 3 ( 8-bit) | User Available (Business audio, LPTx - ECP or EPP mode) |
| DRQ 4 (16-bit) | RESERVED (cascade channel) Memory-(DMA)-REFRESH |
| DRQ 5 (16-bit) | User Available (ISA bus) |
| DRQ 6 (16-bit) | User Available (ISA bus) |
| DRQ 7 (16-bit) | User Available (ISA bus / 6384 P60/D Hard Disk) |
Typical IRQ Assignments
APIC (Advanced Programmable Interrupt Controller) IRQ Assignments (e.g. Netfinity 3500)
System IRQs
Please see the LEGAL - Trademark notice.
Interrupt
Ctrl #1Interrupt
Ctrl #2Assignment
8-bit
16-bit
type
SMI
System/Power Management IRQ
--
NMI
Parity Error or I/O Channel check
--
IRQ 0
Interval Timer
--
IRQ 1
Keyboard bffr.-full
--
IRQ 2
Cascade IRQ-req. (IRQ-8 to IRQ-15)
--
IRQ 8
Real Time Clock
--
IRQ 9
Redirect Cascade to IRQ 2 (User Available)
8/16
IRQ 10
User Available
16
IRQ 11
User Available (2137-SL A - USB)
16
IRQ 12
Auxiliary device (Mouse) (User Available)
16
IRQ 13
Math Coprocessor exception
--
IRQ 14
Hard Disk (Primary IDE)
16
IRQ 15
Secondary IDE (User Available)
Used by NOVELL, if installed. 16
IRQ 3
COM2:
8/16
IRQ 4
COM1:
8/16
IRQ 5
LPT2: / Sound Card
User Available 8/16
IRQ 6
Diskette drive controller
8/16
IRQ 7
LPT1: (User Available, if shareable)
8/16
Interrupt
System resource
IRQ 16
PCI device
IRQ 17
PCI device
IRQ 18
PCI device
IRQ 19
PCI device
IRQ 20
Not available
IRQ 21
Not available
IRQ 22
Not available
IRQ 23
Not available
IRQ 24
SMI (System Management Interrupt)
An IRQ or interrupt request, is the process whereby an input or output device tells the CPU to
temporarily interrupt whatever it is doing and immediately process something from the source of the interrupt.
When finished the CPU goes back to what it was already processing. There are 16 IRQs (IRQ 0 trough IRQ 15) in the ISA bus design.
Devices that need an IRQ line to operate sometimes must have the use of that line exclusively.
Many expansion cards require the use of an IRQ line to operate, e.g. network interface cards and sound cards. When you install
a card that uses an IRQ, it will have a default IRQ setting that you might need to change if that IRQ is already in use and cannot be shared.
There are different ways of setting an IRQ assignment, with jumpers being the most common.
Both the ISA bus and the PCI bus use the same set of system IRQs. For the PCI bus there is an additional consideration. On the PCI bus,
you must assign an IRQ to the PCI slot you will install an IRQ-using card in. There are two methods of generating an IRQ on the PCI bus,
level-triggering (level sensitive) and edge-triggering . Most PCI expansion cards use the level-triggered design. Some very few PCI cards may use
the edge-triggered method. Once more... HW-IRQs are level-sensitive in systems using the PCI bus architecture and are edge-triggered in systems using the
PC-type I/O architecture. The interrupt controller clears its-in service register bit when the interrupt routine sends an End-of-Interrupt EOI
command to the controller. The EOI command is sent regardless of whether the incoming interrupt request to the controller is active or inactive.
In systems using level-sensitive interrupts, the interrupt-in progress latch is readable at an I/O-address bit position. This latch is read during the interrupt service routine and might be reset by the read operation
or it might require an explicit reset.
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