Advantech PCI-1714, User Manual

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PCI-1714 & 1714UL User Manual 32
4.2.6 Pre-Trigger Acquisition Mode
Pre-Trigger mode is a particular application of about-trigger mode. Use
pre-trigger acquisition mode when you want to acquire data before a spe-
cific trigger event occurs. Pre-trigger acquisition starts when you start the
operation and stops when the trigger event happens. Then the specific
number of samples will be reversed in the FIFO before the pre-trigger
event occurred. Please specify the following parameters, after Pre-trigger
Acquisition Mode: has been set.
• The sample clock source and sample rate
• The trigger source
• Assume the total acquired sample number is N, then set the total sample
number to be N+2.
Figure 4.4: Pre-Trigger Acquisition Mode
4.3 A/D Sample Clock Sources
The PCI-1714 cards can adopt both internal and external clock sources
for pacer, post-trigger, delay-trigger, about-trigger acquisition modes:
• Internal A/D sample clock with 8-bit divider
• External A/D sample clock that is connected to either the EXT-CLK0
(the differential clock source) or the EXT_CLK1 (the single ended
clock source) on the ADAM-3909 screw terminal board.
The internal and both external A/D sample clocks are described in more
details in the next pages.