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Chapter 2 Function Reference — DAQ_Config
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National Instruments Corporation 2-119 NI-DAQ FRM for PC Compatibles
Using This Function
DAQ_Config saves the parameters in the configuration table for future data acquisition.
DAQ_Start and SCAN_Start use the configuration table to set the DAQ circuitry to the
correct timing modes.
If both startTrig and extConv are 0, A/D conversions begin as soon as you call
DAQ_Start,
SCAN_Start, or Lab_ISCAN_Start. When startTrig is 1, A/D conversions do not begin
until NI-DAQ receives an external trigger pulse. In the latter case, the Start call merely arms
the device. If you are using all E Series devices, see the
Select_Signal function for
information about the external timing signals. When the A/D conversions have begun (with
the start trigger), the onboard counters control the timing of the conversions. When extConv
is 1, the timing of A/D conversions is completely controlled by the signal applied at the
EXTCONV* input. Again, the Start call merely arms the device, and after you make this
call, the device performs an A/D conversion every time NI-DAQ receives a pulse at the
EXTCONV* input. When extConv is 2, the device performs a multiple-channel scan each
time the device receives an active low pulse at the OUT2 signal (pin 46) of the non-E Series
MIO device I/O connector, or the COUTB1 signal (pin 43) on Lab and 1200 Series devices.
On the MIO-16/16D, you cannot use both external start triggering and external sample clock
(startTrig = 1 and extConv = 1) simultaneously. NI-DAQ returns an error if you try to
configure them simultaneously. On the AT-MIO-16F-5, AT-MIO-64F-5, AT-MIO-16X, E
Series, and Lab and 1200 Series devices, you can configure external start triggering and the
external sample clock simultaneously.
(MIO-16 and Lab and 1200 Series devices only) In most cases, you should not use external
conversion pulses in scanning operations when you are using SCXI in Multiplexed mode.
There is no way of masking conversions before the data acquisition begins, so any conversion
pulses that occur before NI-DAQ triggers the acquisition will advance the SCXI channels.
The AT-MIO-16X and AT-MIO-16F-5 do not have this restriction.
(Lab and 1200 Series devices only) If the device is using an external timing clock for A/D
conversions (extConv = 1), the first clock pulse after one of the three start calls (
AI_Setup,
DAQ_Start, or Lab_ISCAN_Start) is to activate the device for external timing. It does not
generate a conversion. However, all subsequent clock pulses will generate conversions.
(E Series devices only) If you use this function with startTrig = 1, the device waits for an
active low external pulse on the PFI0 pin to initiate the DAQ sequence. If you use this function
with extConv = 1 or 3, the device uses active low pulses on the PFI2 pin for sample-interval
timing. If you use this function with extConv = 2 or 3, the device uses active low pulses on
the PFI7 pin for scan-interval timing. These settings are consistent with the Am9513-based
MIO device selections. You can use the
Select_Signal function instead of this function to
take advantage of the DAQ-STC signal routing and polarity selection features.