Information Technology Reference
In-Depth Information
Figure 2.12
Standard set-up of IRQ lines
IRQ3
: Secondary serial port (COM2:)
The secondary serial port (
COM2:
) uses
IRQ3
to
interrupt the processor. Typically,
COM3:
to
COM8:
also use it, although
COM3:
may use
IRQ4
.
IRQ4
: Primary serial port (COM1:)
The primary serial port (
COM1:
) uses
IRQ4
to
interrupt the processor. Typically,
COM3:
also
uses it.
IRQ5
: Secondary parallel port (LPT2:)
On older PCs the
IRQ5
line was used by the fixed
disk. On newer systems the secondary parallel port
uses it. Typically, it is used by a sound card on
PCs which have no secondary parallel port con-
nected.
IRQ6
: Floppy disk controller
The floppy disk controller activates the
IRQ6
line
on completion of a disk operation.
IRQ7
: Primary parallel port (LPT1:)
Printers (or other parallel devices) activate the
IRQ7
line when they become active. As with
IRQ5
it may be used by another device, if there
are no other devices connected to this line.
IRQ9
Redirected to
IRQ2
service routine.
