July 2003
Beginner to intermediate
874 pages
38h 13m
English
Content preview from PC Hardware in a Nutshell, 3rd Edition
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Interrupt Request Line (IRQ)
When a component or peripheral, such as a network adapter or sound card, needs to get the CPU’s attention, it does so by generating a signal on an Interrupt Request Line (IRQ). Table 1-2 lists IRQs and the devices that typically use them.
Table 1-2. /16/32-bit ISA/PCI standard IRQ assignments
|
IRQ |
Bus type |
Typically used by |
|---|---|---|
|
00 |
none |
Non-maskable Interrupt (NMI); system timer |
|
01 |
none |
Keyboard port |
|
02 |
none |
Programmable Interrupt Controller (PIC); cascade to IRQ 09 |
|
03 |
8/16-bit |
Communications Port 2 (COM2:) |
|
04 |
8/16-bit |
Communications Port 1 (COM1:) |
|
05 |
8/16-bit |
Sound card; printer port (LPT2:) |
|
06 |
8/16-bit |
Floppy disk controller |
|
07 |
8/16-bit |
Printer port (LPT1:) |
|
08 |
none |
System CMOS/real-time clock |
|
09 |
8/16-bit |
Redirected from IRQ 02; network interface |
|
10 |
16-bit |
Network interface; USB host controller |
|
11 |
16-bit |
Video adapter; SCSI host adapter |
|
12 |
16-bit |
PS/2 mouse port |
|
13 |
none |
Numeric data processor (math coprocessor) |
|
14 |
16-bit |
Primary IDE interface |
|
15 |
16-bit |
Secondary IDE interface |
An 8-bit ISA slot contains physical IRQ lines only for IRQ 02 through IRQ 07 because IRQ 00 and IRQ 01 are reserved for system functions. A 16-bit ISA slot contains physical IRQ lines for IRQs 03 through 07, 09 through 12, 14, and 15. IRQ 09 is mapped to IRQ 02, allowing 8-bit ISA cards to recognize IRQ 09 as IRQ 02. IRQs 00, 01, 02, 08, and 13 are not present in any slot, and so cannot be assigned to devices.
If the processor receives ...
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