3C90x - 3C59x - 3C339 - Changing the IRQ

Changing the Interrupt Request (IRQ) for the 3c90x Family of NICs

NOTE: This document uses the 3C90x NIC family as an example, but can be applied to the 3C59x family and
the 3C339 NIC.

3Com's EtherLink XL and Fast EtherLink XL family of NICs (3C905-TX, 3C905-T4, 3C900-COMBO & 3C900-TPO)
are the PCI 2.1 compliant adapters installed in the system's small, white expansion slots. The slots usually reside
on the PCI bus.

Should the IRQ Be Changed?

NOTE: 3Com recommends assigning its NICs to IRQs 10, 11 or 12 because these are often unused.
IRQs 2, 9, and 15 are not recommended because they are often used by other PCI devices.

NOTE: NICs must be installed in slots that support busmastering, and busmastering must be enabled
within the BIOS.

NIC IRQs should be changed to avoid conflict with other PCI devices. Although 3Com NICs support IRQ sharing,
other PCI devices may not support this function. Sharing IRQs with these devices may cause one or more of the
symptoms listed below:

Hanging, freezing, or locking at bootup, or when accessing another PCI device.
Slow performance.
Absence of video.
No logon available.
Blue screen in Windows NT.

Background:

When the system boots, BIOS recognizes NICs, and other attached PCI devices, and assigns resources, such as
IRQs, I/O, and memory, to these devices. IRQ assignments depend on:

The presence of devices, such as video, SCSI, sound, modem, etc. The BIOS finds out what resources each
PCI device needs and assigns the resources as it sees fit. The BIOS assigns resources to all PCI devices,
whether they are part of the motherboard or installed in a PCI slot.

The system's setup. Because BIOS is customized to the particular system's configuration, systems with the
same BIOS version, but different configurations, may handle the allocation of resources differently.

The PCI devices cannot request specific resources or control the manner in which the BIOS assigns resources.
Resources cannot be jumpered or soft-set by any type of software, including Windows 95, Windows NT or the 3Com Configuration & Diagnostics program.

To Change the IRQ for the 3c90x Family of NICs:

NOTE: If you have questions about configuring IRQs in your system's BIOS, refer to the system's documentation,
or contact your dealer or the system's manufacturer.

NOTE: You cannot manually configure NIC IRQs in Windows 95 or NT. The nature of the PCI device causes the system to display one of the following messages:

In Windows 95 - This resource setting cannot be modified.
In Windows NT - Cannot configure the software component.

In systems with user-configurable PCI settings:

Configure the NICs' IRQs using the BIOS or CMOS utility, a.k.a. the Setup Utility. (Refer to your motherboard vendor,
the computer's documentation, or start the CMOS setup program, for information on the options available.)

The program is usually accessible immediately after the system boots. You may need to use a pre-determined key
or set of keys, i.e. F10, DEL, SHIFT-ALT-ENTER, etc., to access the utility.

In systems without user-configurable PCI settings:

Move the PCI card to a different slot. Sometimes the move causes the system to assign a different IRQ to the card.
Update the BIOS. Sometimes a newer BIOS will allow the user to configure the PCI resources.

To Troubleshoot IRQ Conflicts:

Examine the system BIOS.
Move the NIC to a different slot.
Isolate the conflict by removing other PCI devices, such as Video, SCSI, modem, etc.
Try an ISA video adapter.

To View IRQs in the Operating System:

For Windows 95
Right-Click on MY COMPUTER.
Click on PROPERTIES.
Click on DEVICE MANAGER.
Double-click on COMPUTER.
View the 3Com NIC via an Interrupt setting on this screen.

For Windows NT 4.0
Go to START, then PROGRAMS, then ADMINISTRATIVE TOOLS.
Click on WINDOWS NT DIAGNOSTICS.
Click on RESOURCES.
Click on IRQ.
View the 3Com NIC via an Interrupt setting, such as El90x.

For DOS 6.x
Type MSD in your DOS directory.

Keywords: Change IRQ, Resource Conflict, Change Interrupt, Configuration, Change the IRQ