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Chapter 4 Register-Level Programming
© National Instruments Corporation 4-7 Lab-NB User Manual
Bit Name Description (continued)
8 PRETRIG Pretrigger Bit—This bit is used to set the pretriggering feature on
the Lab-NB. It also supersedes any setting in the EXTTRIGEN bit
described earlier. If PRETRIG is cleared, then the function of the
EXTTRIG line on the I/O connector is determined by
EXTTRIGEN. If PRETRIG is set, then the EXTTRIG line
becomes a pretrigger. In pretrigger operation, the sample counter
(counter A1) does not begin decrementing until a rising edge is
detected on EXTTRIG. When the conversion sequence terminates,
some of the acquired data has been received before the trigger
signal and some has arrived after the signal. The number of
samples after the trigger is the value loaded into the sample
counter (counter A1), but the number of samples before the trigger
depends on the arrival time of the trigger signal.
7 SCANEN Scan Enable Bit—This bit enables or disables multichannel
scanning during data acquisition. If this bit is set, analog channels
MA<2..0> through 0 are sampled alternately. If this bit is cleared,
a single analog channel specified by MA<2..0> is sampled during
the entire DAQ operation. See Programming Multiple A/D
Conversions with Channel Scanning later in this chapter for the
correct sequence involved in setting this bit. For example, if
MA<2..0> is 011 and SCANEN is set, analog input channels 3
through 0 are sampled alternately during subsequent data
conversions. If SCANEN is then cleared (with MA<2..0> still set
to 011), only analog input channel 3 is sampled during the
subsequent data conversions.
6–4 MA<2..0> Multiplexer Address Bit—These three bits select which of the
eight input channels are read. The analog input multiplexer
depends on these three bits to select the input channel. The input
channel is selected as follows:
MA<2..0> Selected Channel
000
001
010
011
100
101
110
111
0
1
2
3
4
5
6
7
If SCANEN is set, analog channels MA<2..0> through 0 are
sampled alternately. If SCANEN is cleared, a single analog
channel specified by MA<2..0> is sampled during the entire DAQ
operation. See Programming Multiple A/D Conversions with