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Chapter 2 Function Reference — SCAN_Start
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National Instruments Corporation 2-311 NI-DAQ FRM for PC Compatibles
0: External clock used as timebase (Connect your own timebase frequency to the
internal scan-interval counter via the SOURCE5 input for the MIO devices or,
by default, the PFI8 input for the E Series devices).
1: 1 MHz clock used as timebase (1 µs resolution) (non-E Series only).
2: 100 kHz clock used as timebase (10 µs resolution).
3: 10 kHz clock used as timebase (100 µs resolution) (non-E Series only).
4: 1 kHz clock used as timebase (1 ms resolution) (non-E Series only).
5: 100 Hz clock used as timebase (10 ms resolution) (non-E Series only).
On E Series devices, if you use this function with sampleTimebase set to 0 must call the
Select_Signal function with signal set to ND_IN_CHANNEL_CLOCK_TIMEBASE and
source set to a value other than
ND_INTERNAL_20_MHZ and ND_INTERNAL_100_KHZ before
calling
SCAN_Start with sampleTimebase set to 0; otherwise, SCAN_Start will select
low-to-high transitions on the PFI8 I/O connector pin as your external sample timebase.
If sample-interval timing is to be externally controlled (extConv = 1 or 3, see
DAQ_Config),
NI-DAQ ignores the sampTimebase parameter, which can be any value.
On DSA devices, sampTimebase is ignored. Use
DAQ_Set_Clock
to set the can rate.
sampInterval indicates the length of the sample interval (that is, the amount of time to elapse
between each A/D conversion within a scan sequence).
Range: 2 through 65,535.
The sample interval is a function of the timebase resolution. The actual sample interval in
seconds is determined by the following formula:
sampInterval
*
(sample timebase resolution)
where the sample timebase resolution is equal to one of the values of sampTimebase as
specified above. For example, if sampInterval = 25 and sampTimebase = 2, the actual
sample interval is 25
*
10 µs = 250 µs. The time to complete one scan sequence in seconds is
(the actual sample interval)
*
(number of channels scanned). If the sample interval is to be
externally controlled, the sampInterval parameter is ignored and can be any value.
On DSA devices, sampInterval is ignored. Use
DAQ_Set_Clock
to set the scan rate.
scanTimebase selects the clock frequency that indicates the timebase, or resolution, to be
used for the scan-interval counter. The scan-interval counter controls the time that elapses
between scan sequences. scanTimebase has the following possible values:
–3: 20 MHz clock used as a timebase (50 ns resolution) (E Series only).
–1: 5 MHz clock used as timebase (200 ns resolution) (AT-MIO-16F-5,
AT-MIO-64F-5, and AT-MIO-16X only).
0: External clock used as timebase (Connect your own timebase frequency to the
internal scan-interval counter via the SOURCE5 input for the MIO devices or,
by default, the PFI8 input for the E Series devices).