Figure 310. posttrigger daq timing, Figure 3-10, Posttrigger daq timing -20 – National Instruments PCI-1200 User Manual
Page 42: Figure 3-10. posttrigger daq timing
Chapter 3
Signal Connections
3-20
© National Instruments Corporation
of EXTCONV*. Further transitions on the EXTTRIG line have no effect
until a new DAQ sequence is established.
Figure 3-10 shows a possible controlled DAQ 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*.
Figure 3-10. Posttrigger DAQ Timing
In the PRETRIG mode, EXTTRIG serves as a pretrigger signal. Data is
acquired both before and after the EXTTRIG signal occurs. A/D
conversions are software enabled, which initiates the DAQ operation.
However, the sample counter is not started until the EXTTRIG input senses
a rising edge. 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.
Figure 3-11 shows a pretrigger DAQ timing sequence using EXTTRIG and
EXTCONV*. The DAQ operation has been initiated through software.
Notice that the sample counter has been programmed to allow five
conversions after the rising edge on the EXTTRIG signal. Additional
transitions on the EXTTRIG line have no effect until you initiate a new
DAQ sequence.
t
w
50 ns minimum
EXTTRIG
V
IH
V
IL
t
w
EXTCONV*
CONVERT
t
d
50 ns minimum
t
w
t
d