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Chapter 2 Function Reference — SCAN_Start
NI-DAQ FRM for PC Compatibles 2-310
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National Instruments Corporation
2 through 2
24
*
(total number of channels scanned) or 2
32
– 1, whichever is less
for E Series and DSA devices. For PCI-611X devices, count must be EVEN.
count must be an integer multiple of the total number of channels scanned. count refers to
the total number of A/D conversions to be performed; therefore, the number of samples
acquired from each channel is equal to count divided by the total number of channels
scanned. This number is also the total number of scans. For the E Series devices, the total
number of scans must be at least 2. If you do not use external multiplexer (AMUX-64T)
devices, the total number of channels scanned is equal to the value of numChans (see
Scan_Setup).
If you use one or more external multiplexer devices with any MIO or AI device except the
MIO-64, the total number of channels scanned equals (four-to-one multiplexer)
*
(number of
onboard channels scanned)
*
(scanned)
*
(number of external multiplexer devices), or the
total number of channels scanned equals (4)
*
(numChans)
*
(num_mux_brds). For example,
if you use one AMUX-64T and scan eight onboard channels, the total number of channels
scanned equals (4)
*
(8)
*
(1) = 32.
If you use one or more external multiplexer devices (AMUX-64Ts) with the MIO-64, the total
number of channels scanned equals (4)
*
(numChans1)
*
(num_mux_brds) + numChans2,
where:
• 4 represents a four-to-one multiplexer.
• numChans1 is the number of onboard channels (of an MIO or AI connector, the first
connector) scanned.
Range: 0 through 7 differential, 0 through 15 single-ended.
• num_mux_brds is the number of external multiplexer devices.
• numChans2 is the number of onboard channels (of an analog connector, the second
connector) scanned.
Range: 0 through 23 differential, 0 through 48 single-ended.
If you use SCXI, the total number of channels scanned is the total number of channels
specified in the
SCXI_SCAN_Setup call.
sampTimebase selects the clock frequency that indicates the timebase, or resolution, to be
used for the sample-interval counter. The sample-interval counter controls the time that
elapses between acquisition of samples within a scan sequence.
sampTimebase 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).