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Resolve IRQ Conflicts in
Hardware Device: Tech Support Page!
By Raymond Garcia
Resolve IRQ Conflict in Windows: Serial or Parallel Ports - If you've
installed a new card, serial or parallel device and
it's not working, the new port may be trying to use
an IRQ setting assigned to more then one device or
an old port. You can disable the existing ports via
the Control Panel. When a hardware device needs the
CPU to do something, such as when the keyboard needs
a keystroke to be processed, the device passes a number,
called an interrupt request number or IRQ,
to the CPU.
During the boot process, a unique IRQ
is assigned to each hardware device that requires
one, and uniquely identifies that device as wall as
the software that controls it. A device requires an
IRQ if it can initiate an action or provide input
to the computer. Some devices that are assigned IRQs
include the disk drive, the mouse, and keyboard. The
CPU uses an IRQ to identify the peripheral and find
the software that controls it.
A conflict can occur if more then one
device is assigned the same IRQ or I/O address during
the POST. These conflicts are resolved on older expansion
cards by changing DIP switches or jumper settings.
This change causes the card to request an alternative
IRQ or I/O address. For example , if a scanner card
and a network card both request IRQ 10, then there
is a conflict.
Startup BIOS or the OS cannot write
the memory address of the network drive in the same
I/O address location associated with IRQ 10 if the
memory address of the scanner drive is already written
there. If this were to happen, and the scanner asked
for service by sending IRQ 10 to the CPU, the CPU
would respond with a network drive.
In this case, probably neither the scanner
nor the network card would work. If you encounter
a conflict, check both cards. Most likely one of them
has a jumper that you can set so that the card request
an IRQ other than 10.
With newer cards, called Plug-and-play
cards, instead of having to set DIP switches and jumpers
to identify information about hardware and its configuration,
the startup BIOS automatically chooses the resources
(such as IRQ or I/O addresses) that are assigned to
the card. Because the BIOS can select the resources,
conflicts are easily resolved using Plug-and-Play
cards. Of course, the BIOS must be the kind that manage
Plug-and-Play devices and is called Plug-and-Play
BIOS. The OS must also be Plug-and-Play.
1. Right click on My Computer, then
click on properties, then click on Device Manager.
Or, click on Start, point to Settings, and then click
Control Panel, Double-click System, and then click
the Device Manager tab to display all devices.
2. An exclamation point ( ! )
in a yellow circle will appear next to the names of
ports or device that are conflicting. Click the (+)
sign next to Ports (COM and LPT) to display current
3. You can move any devices from the
conflicting ports to the new ports. or move the conflicting
card to an new card slot. Then restart the computer,
Windows should now detect the new attached devices.
4. Double-click the names of the conflicting
COM or LPT ports. Click the check box by "Disable
in this hardware profile."
7. Click OK, and then restart the computer.
Windows should now detect the new serial or parallel
ports and the attached devices.
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