Hardware Configuration and Installation
Chapter 2
VME-AT2000/NI-VXI MS-DOS Getting Started
2-6
© National Instruments Corporation
Interrupt Level Selection
The AT-MXI interface board can use either one or two of the eleven interrupt levels of the PC
AT I/O channel. Setting up an interrupt level for operation involves two steps. First you select
the interrupt level by arranging the jumpers on an array of pins. Next you enable the interrupt
level in the system software.
Note:
You must enable the interrupt levels in the system software before they can
function. If you do not enable the interrupt level, that level will not be driven and
can be used by other devices, regardless of the positions of the jumpers.
Interrupt levels are selected by the position of two jumpers on the 3 by 11 array of pins labeled
W3, located above the I/O card-edge connector on the AT-MXI (refer to Figure 2-1). Use the
jumper farther from the card-edge connector to select the PC AT interrupt level that will convey
board status and error information. Remember to enable this level, or board interrupt, in the
system software for the AT-MXI to function properly. The factory default setting is level 12 and
is enabled on this level by the default configuration software.
Use the jumper on the W3 pin array closer to the I/O card-edge connector to select which PC AT
interrupt level corresponds to the MXIbus interrupt signal IRQ*. Because the MXIbus interrupt
is also one of the conditions covered by the other jumper, you normally do not need to use a
separate interrupt level for the MXIbus IRQ* signal; it is useful only if you want a different
interrupt vector or priority for MXIbus interrupts. This jumper is set at the factory to a default
level of 10.
Note:
The AT-MXI does not have the ability to share interrupt levels with other devices.
If you select an interrupt level by placing a jumper on a particular level and enable
that level in software, no other device in the system can use that level. Make sure
that no other devices in your system use the interrupt level(s) selected and enabled
for use by the AT-MXI. If they do, change the interrupt level(s) of either the
AT-MXI or the other devices. If you change an AT-MXI interrupt level, make a
corresponding change to the AT-MXI configuration software as described in the
Configuring the NI-VXI Software section of Chapter 3.
The AT-MXI can use interrupt levels IRQ3, 4, 5, 6, 7, 9, 10, 11, 12, 14, and 15. Be careful when
re-assigning interrupt levels on the AT-MXI. Notice that most PC ATs use interrupt level 6 for
the diskette drive controller and interrupt level 14 for the hard disk drive controller. Other
interrupt levels might be used by standard logic devices on the motherboard so check your
computer documentation before changing interrupt levels.
