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About Fast Data Channel (FDC) Operation
VX4101A MultiPaq Instrument User Manual
2–19
Since the DMM and DAC only have 1 FDC channel, the list returned by either
device contains a single channel value. This physical FDC channel number is
passed to the host FDC drivers through the Host session with a viSetAttribute
command. Use the following command syntax:
viSetAttribute (vi, attribute, attribute state);
Example Code for Passing Values to the Drivers. You can use the following
sample code to pass the channel values to the FDC drivers:
errs = viSetAttribute (fdc, VI_ATTR_FDC_CHNL,
fdc_physical_channel);
The Commander and Servant FDC drivers are now assigned to the same physical
channel.
Other FDC attributes may also be specified. The host computer vendor’s FDC
support documentation will detail all the configuration parameters required for
your FDC driver implementation.
After the FDC drivers are configured, you must command the servant device to
open the logical FDC channel associated with its physical channel. The
FDC:SEL? query returns the currently selected logical fdc channel:
errs = viWrite (wsp, "VXI:FDC:SEL?", 12, &RetCnt);
errs = viRead (wsp, buff, sizeof(buff), &RetCnt);
fdc_logical_channel = atoi(buff);
NOTE. For the VX4101A DAC and DMM, the above query always returns a 1.
You do not need to use this query.
The Open command opens the selected FDC channel in the selected mode, in
this case, Read/Write.
Example Code for Opening the Channel.
sprintf(buff,"VXI:FDC:OPEN RW %u",fdc_logical_channel);
errs = viWrite (wsp, buff, strlen(buff), &RetCnt);
The VX4101A is comprised of a number of independently operating instruments.
The previous OPEN command requires the servant device to set up and initialize
some of the instrument’s internal resources. The time it takes to complete this
Other Attributes
Opening the FDC Channel