Figure 3-13. Posttrigger Daq Timing - National Instruments DAQCard-1200 User Manual

V IH
EXTTRIG
V IL
EXTCONV*
CONVERT
© National Instruments Corporation
In the posttrigger mode, EXTTRIG serves as an external trigger that
initiates a data acquisition sequence. When you use counter A0 to time
sample intervals, a rising edge on EXTTRIG starts counter A0 and the data
acquisition sequence. When you use EXTCONV* to time sample intervals,
data acquisition is enabled on a rising edge of EXTTRIG followed by a
rising edge on EXTCONV*. The first conversion occurs on the next falling
edge of EXTCONV*. Further transitions on the EXTTRIG line have no
effect until a new data acquisition sequence is established.
Figure 3-13 shows a possible controlled data acquisition sequence using
EXTCONV* and EXTTRIG. The rising edge of EXTCONV* that enables
external conversions must occur a minimum of 50 ns after the rising edge
of EXTTRIG. The first conversion occurs on the next falling edge of
EXTCONV*.
t w
t w

Figure 3-13. Posttrigger DAQ Timing

In the pretrigger mode, EXTTRIG serves as a stop-trigger signal. Data is
acquired both before and after the stop trigger occurs. A/D conversions are
software enabled, which initiates the data acquisition operation. However,
the sample counter is not started until a rising edge is sensed on the
EXTTRIG input. Conversions remain enabled until the sample counter
counts to zero. The maximum number of samples acquired after the stop
trigger is limited to 65,535. The number of samples acquired before the
trigger is limited only by the size of the memory buffer available for data
acquisition.
t w 50 ns minimum
t d 50 ns minimum
t d
3-23
Chapter 3 Signal Connections
DAQCard-1200 User Manual