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Chapter 2

Function Reference — DAQ_Config

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 National Instruments Corporation

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NI-DAQ FRM for PC Compatibles

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.