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Chapter 3 Connecting the Signals
© National Instruments Corporation 3-25 DAQCard-1200 User Manual
Figure 3-15.
Pretrigger DAQ Timing
Because both pretrigger and posttrigger modes use EXTTRIG input, you
can only use one mode at a time. Therefore, you cannot use both a hardware
start and a hardware stop trigger during the same acquisition.
Figure 3-16 shows an example of a multiple-channel interval-scanning
DAQ operation. The scan interval and the sample interval are being timed
externally through OUTB1 and EXTCONV*. Channels 1 and 0 of the input
multiplexers are being scanned once during each scan interval. The first
rising edge of EXTCONV* must occur a minimum of 50 ns after the rising
edge on OUTB1. The first rising edge of EXTCONV* after the rising edge
of OUTB1 enables an internal GATE signal that allows conversions to
occur. The first conversion then occurs on the following falling edge of
EXTCONV*.
Instead of using counter B1, you can externally time the scan interval
through OUTB1. If you externally time the sample interval, you should also
externally time the scan interval.
CONVERT
EXTCONV*
EXTTRIG
V
IH
V
IL
t
w
t
w
t
w
50 ns minimum
First posttrigger sample