Chapter 2
Configuration and Startup Procedures
©
National Instruments Corporation
2-19
SC Servants. After this, the GPIB-VXI/C RM and general configuration
operations are complete.
GPIB Address Assignment
The GPIB-VXI/C automatically assigns GPIB addresses—primary or
secondary—to itself and to each of its immediate Message-Based SC
Servants. If the Message-Based device does not support minimal Word
Serial[I] or VXIbus 488.2[I4] capabilities, no GPIB address link is created.
The GPIB-VXI/C assigns a GPIB address to each device according to the
top five bits of its logical address. For example, the GPIB address of a
device with Logical Address 96 (01100000b) would be 12 (01100b).
If two or more devices have logical addresses with the same top five bits,
the GPIB-VXI/C assigns GPIB addresses to devices in order of the least
significant three bits. Conflicting devices are given the next available GPIB
address. For example, if the GPIB-VXI/C and its Message-Based Servants
have Logical Addresses 0, 24, 27, and 33, the GPIB-VXI/C assigns GPIB
addresses as shown in Table 2-10.
In the example shown in Table 2-10, the device at Logical Address 27
was assigned GPIB Address 5 because addresses 3 and 4 were previously
assigned. By spacing the GPIB-VXI/C Message-Based Servants at
intervals of eight logical address locations you can avoid situations in
which removing or adding one device changes the GPIB address of another
device.
The default configuration for the GPIB-VXI/C is to use multiple GPIB
secondary addresses (not multiple primary addresses). You can change
the configuration to use multiple primary addresses through nonvolatile
memory configuration as described in the
section of Chapter 4,
Table 2-10.
Example GPIB Address Assignment
Logical Address
3 LSB (Order
of Assignment)
5 MSB
GPIB Address
Decimal
Binary
Binary
Binary
Decimal
0
00000000b
000b
00000b
0
24
00011000b
000b
00011b
3
33
00100001b
001b
00100b
4
27
00011011b
011b
00011b
5
