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Chapter 2 Function Reference — SCXI_Track_Hold_Setup
NI-DAQ FRM for PC Compatibles 2-370
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National Instruments Corporation
DAQdeviceNumber is the device number of the DAQ device in the PC that will be used to
acquire the data. If the DAQdeviceNumber specified is a Lab and 1200 Series devices,
DAQCard-700, or LPM device, inputMode 2 is not supported. If you are using the
SCXI-1200 to acquire the data, use the logical device number you assigned to the SCXI-1200
in the configuration utility.
Using This Function
For single channel operations (inputMode = 1) the module is level-sensitive to the source
signal; that is, when the source signal is low the module is in track mode, and when the
source signal is high the module is in hold mode. If source = 0, you can use calls to
SCXI_Track_Hold_Control function to put the module into track or hold mode by
toggling the output of the appropriate counter on the DAQ device. If the SCXI-1140 you want
to read is not cabled to the DAQ device, you will have to configure the SCXI-1140 module
that is cabled to the DAQ device to send the counter output on the SCXIbus to the module you
want. Then the
SCXI_Track_Hold_Control call can put the module you want into track or
hold mode. The
SCXI_Track_Hold_Setup parameters for each module would be:
• For the SCXI-1140 that is cabled to the DAQ device as follows:
inputMode = 1
source = 0
send = 2
• For the SCXI-1140 module to be read:
inputMode = 1
source = 2
send = 0
Using an external source (source = 1) for single channel operations is not normally useful
because NI-DAQ has no way of determining when the module has gone into hold mode and
it is appropriate to read the channels.
(MIO, Lab-PC-1200, Lab-PC-1200AI, Lab-PC+, PCI-1200, SCXI-1200, and
DAQCard-1200 only) For interval channel scanning operations (inputMode = 2) NI-DAQ
configures the module to go into hold mode on the rising edge of the source signal. If
source = 0, that will happen when counter 2 on the Am9513-based MIO devices, a dedicated
DAQ-STC counter on E Series devices, or counter B1 on the Lab-PC-1200, Lab-PC-1200AI,
Lab-PC+, PCI-1200, SCXI-1200, or DAQCard-1200 pulses at the beginning of each scan
interval; if source = 1, that will happen on the rising edge of the external signal connected to
HOLDTRIG on the module front connector. In the latter case, you should configure the DAQ
device for external scan interval timing (using the
DAQ_Config function) so that the external
signal will trigger each scan. To scan more than one SCXI-1140, you can send the source
signal from the module that is receiving it (either from the counter or from HOLDTRIG) to
the other modules over the SCXIbus. Notice that the module that is cabled to the device can