Installation and Configuration Section Two
GPIB-PC User Manual 2-16 ©National Instruments Corp.
DMA Channel (Boards Only)
This field appears only on computers supporting DMA capability. The
GPIB-PC may use any of the three DMA channels, 1, 2, or 3, provided
that another device is not already using that channel. If a DMA channel
is not available, programmed I/O can be enabled by selecting NONE.
Internal Clock Frequency (Boards Only)
For the GPIB-PCII, this value is equal to the frequency of the PC bus
signal OSC divided by 2 and rounded up. Since OSC is fixed at 14.14
MHz for all IBM PCs and compatibles, this field is always set to 8.
For the GPIB-PCIIA, this value is equal to the frequency of the PC bus
signal CLK and rounded up. Since the signal CLK varies according to
the machine, this field varies as well. Typical examples are:
Machine PCII ICF value PCIIA ICF value
IBM PC, XT, and compatibles 8 5
IBM XT (new) 8 8
IBM AT and compatibles 8 6
Compaq Deskpro 8 5,8
Compaq Deskpro 286 8 6,8
Compaq Portable 286 8 6,8
Notice that on some computers the CLK frequency depends on whether
the CPU is operated at normal or high-speed mode. If you want to
operate the GPIB-PC under both modes, either reconfigure the software
or use the higher value. If you are in doubt as to what value to enter,
use 8.
Exiting IBCONF
Once all changes have been made, you may exit IBCONF by typing the
function key indicated on the screen. The program will first ask if it
should save any changes before exiting. Typing a y response causes the
changes to be written to the file on disk. Before exiting, the program
will check for situations that may cause problems.
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