Installation and Configuration Section TwoGPIB-PC User Manual 2-16 ©National Instruments Corp.DMA Channel (Boards Only)This field appears only on computers supporting DMA capability. TheGPIB-PC may use any of the three DMA channels, 1, 2, or 3, providedthat another device is not already using that channel. If a DMA channelis 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 bussignal OSC divided by 2 and rounded up. Since OSC is fixed at 14.14MHz 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 bussignal CLK and rounded up. Since the signal CLK varies according tothe machine, this field varies as well. Typical examples are:Machine PCII ICF value PCIIA ICF valueIBM PC, XT, and compatibles 8 5IBM XT (new) 8 8IBM AT and compatibles 8 6Compaq Deskpro 8 5,8Compaq Deskpro 286 8 6,8Compaq Portable 286 8 6,8Notice that on some computers the CLK frequency depends on whetherthe CPU is operated at normal or high-speed mode. If you want tooperate the GPIB-PC under both modes, either reconfigure the softwareor use the higher value. If you are in doubt as to what value to enter,use 8.Exiting IBCONFOnce all changes have been made, you may exit IBCONF by typing thefunction key indicated on the screen. The program will first ask if itshould save any changes before exiting. Typing a y response causes thechanges to be written to the file on disk. Before exiting, the programwill check for situations that may cause problems.
