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Chapter 2
Configuration and Installation
©
National Instruments Corporation
2-3
VXIbus Logical Address
Each module in a VXIbus system is assigned a unique number between
0 and 254. This 8-bit number, called the
logical address
, defines the base
address for the VXIbus configuration registers located on the module. With
unique logical addresses, each VXIbus module in the system is assigned
64 bytes of configuration space in the upper 16 KB of the A16 address
space.
Logical address 0 is reserved for the Resource Manager in the VXIbus
system. Because the VXI-AO-48XDC cannot act as a Resource Manager,
do not configure the VXI-AO-48XDC with a logical address of 0. The
factory-default logical address for the VXI-AO-48XDC is
5
.
Some VXIbus modules have dynamically configurable logical addresses.
These modules have an initial logical address of hex FF or decimal 255,
which indicates that they can be dynamically configured.
The VXI-AO-48XDC supports dynamic configuration of its logical
address. However, adding or removing modules can change the logical
address of the VXI-AO-48XDC. Tracking these changes in your
application software can be troublesome.
In many cases, static configuration of the logical address is easier. For
example, ensure that no other statically configurable VXIbus modules have
a logical address of
5
. If they do, change the logical address setting of either
the VXI-AO-48XDC or the other module so that every module in the
system has a different logical address.
To change the VXI-AO-48XDC logical address, modify the setting of the
8-bit DIP switch labeled
Logical Address Switch
(see Figure 2-1 for the
switch location). The
down
position of the DIP switch corresponds to a
logic value of
0
and the
up
position corresponds to a logic value of
1
. Verify
that the VXI-AO-48XDC does not have the same logical address as any
other statically configured VXIbus module in your system.
Note
Logical address 0 is
not
allowed for the VXI-AO-48XDC.