Chapter 2
Hardware Configuration and Installation
© National Instruments Corp.
2-3
AT-GPIB for SCO UNIX
Base I/O Address Selection
The base I/O address is determined by the switches at position U25. The
switches are set at the factory for the base I/O address 2C0 hex. The
AT-GPIB board uses the I/O address space 2C0 through 2DF hex with this
setting. If you install more than one AT -GPIB board in your computer,
each board must be configured to use a unique base I/O address. The
default AT-GPIB board base I/O addresses for the NI-488M software are
shown in Table 2-2. You must change the base I/O address setting in the
hardware to match the software base I/O address setting.
Table 2-2. Software Default AT-GPIB Base I/O Addresses
Board
Default
Base I/O Address
First AT-GPIB (
gpib0
)
260 hex
Second AT-GPIB (
gpib1
)
240 hex
Check to determine that the software default I/O address space is not
already used by other equipment installed in your computer. If any
equipment in your computer uses this I/O address space, change the base
I/O address of either the AT-GPIB board or the other device. (See
Table 2-3 later in this chapter for other possible AT-GPIB board base I/O
address settings.)
Each switch in U25 corresponds to one of the PC AT bus address lines A9
through A5. The top switch (
1
) corresponds to address line A9, the next
switch from the top (
2
) corresponds to address line A8, and so on. The five
least significant bits of the address (A4 through A0) are used by the
AT-GPIB board to select the appropriate GPIB adapter register and cannot
be changed; therefore, bits A4 through A0 are always 00000 (binary) when
determining the base I/O address.
Press down on the side marked 1 to select a binary value of 1 for the
corresponding address bit. Press down on the side marked 0 to select a
binary value of 0 for the corresponding address bit (refer to Figure 2-2).
Figure 2-2 shows the hardware default base I/O address setting and the
setting to which you must change your hardware to match the software base
I/O address default setting. In this figure, the black side of the switch is the