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Chapter 7 Troubleshooting 71
Error Occurs at Computer Powerup
If an error occurs at boot up, either the Interface is not installed properly or there is an
address or interrupt conflict. Turn off the computer, try a new address or interrupt and
reinstall the card. Be sure the Interface card is firmly mounted in the slot.
Since interrupts and DMA channels cannot be shared, make sure no other boards in your
computer use this interrupt or these DMA channels.
Conflicts
One of the many advantages that PCI offers over ISA is that the whole issue of address and
interrupt assignments is user transparent and under BIOS control. As a result, users
typically do not have to be concerned about jumpers or switches when installing a PCI
card. Nothing more should be required than to plug in the card, make the connections, and
operate the system. As it turns out, however, in certain situations conflicts may nevertheless
occur and user intervention will be required to resolve them.
Typical PCI motherboards have both ISA and PCI slots and will have both PCI and ISA
cards installed. In the case of the ISA cards, the I/O address and Interrupt assignments
will have been made by you and the BIOS will not know which addresses and interrupts
have been user assigned. When a PCI card is installed, the BIOS checks for available
addresses and interrupt levels and automatically assigns them so that there are no PCI
address or interrupt conflicts. However, because the BIOS doesn't know about the user-
assigned ISA I/O address and interrupt level assignments, it is possible that a PCI card
will be assigned an address or interrupt that is already assigned to an ISA card. If this
happens, improper operation will result. Specifically, the problems could range from
erratic operation under specific conditions to complete system failure. If such a conflict
occurs, because you have no control over the PCI address and interrupt assignments,
there will be no recourse but to examine the ISA assignments and change them to values
which do not conflict. Most (but by no means all) ISA cards make provision for selecting
alternative I/O addresses and interrupt levels so that conflicts can be resolved. Software
is available to help identify specific conflicts.
The following example may serve to illustrate the problem. Suppose you had a system
with an ISA network card, a PCI video card and an ISA sound card. Further, suppose that
you were then going to install a PCI Serial Buffer card. Before installing the PCI Serial
card, the I/O address and interrupt assignments for the installed cards might be as
follows.
Slot Type
Status
I/O Address
Interrupt
1 (ISA)
ISA Network Card
200-210
11
2 (PCI)
PCI Video Card
FF00-FFFF
15
3 (ISA)
ISA Sound Card
300-304
9
4 (PCI)
Empty
N/A
N/A
Table 7. I/O Address & Interrupt Assignments before Installing Serial Card
CAUTION