Analog Triggering - National Instruments PCI E Series Programmer's Manual

Analog Triggering

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the SCAN counter—the pretrigger count and the posttrigger count. To
begin with, the pretrigger count is loaded into the SC. Acquisition is then
started through either software by strobing a bit, or through hardware by
externally pulsing the START1 pin of the connector. Acquisition then starts
and data is acquired. When the SC counts down to zero, the scans continue
and data still gets acquired. During this time, the board waits for a START2
pulse but the SC does not count. Also, the SC gets loaded with the
posttrigger count. When a START2 pulse is received, the SC once again
starts counting. When it reaches zero, the operation ends. Refer to the
Acquisition Level Timing and Control section of Chapter 2 in the DAQ-STC
Technical Reference Manual for timing examples of pretrigger and
posttrigger modes.
Variations:
• Posttrigger and pretrigger modes can be retriggerable. This means
that after one posttrigger or pretrigger operation is over, the SC gets
reloaded and the board sits waiting for an additional START1. This
can continue indefinitely and can be disabled through software.
• A special mode in the DAQ-STC allows continuous software-initiated
acquisition to continue indefinitely. In this mode, the SC gets reloaded
each time it counts down to zero. The acquisition can be stopped by
disarming the SC. When the SC counts down to zero, acquisition stops.
All PCI E Series boards except the PCI-MIO-16XE-50, PCI-6023E,
PCI-6024E, and PCI-6025E have an analog trigger in addition to the digital
triggers. To use analog triggering to start an acquisition sequence, select
either the PFI0/Trig1 input on the I/O connector or one of the analog input
pins. An analog input pin allows you to apply gain to the external signal for
more flexible triggering conditions. The INT/EXTTRIG bit in the Misc.
Command Register selects the source. PFI0/Trig1 pin has an input voltage
range of ±10 V.
An 8-bit serial DAC sets each of the high and low thresholds in the
PCI-MIO-16E-1, PCI-6071E, and the PCI-MIO-16E-4. For the
PCI-MIO-16XE-10, PCI-6031E, PCI-6032E, and PCI-6033E, a 12-bit
serial DAC sets each of the high and low thresholds. These thresholds are
within plus/minus full scale. The selected input is compared against each
of these thresholds by a comparator. The outputs of the comparators are
connected to the DAQ-STC analog trigger inputs 0 and 1. Within the
DAQ-STC, these signals can be routed to any of the internal timing signals.
You can trigger on either a positive or negative slope or on absolute values.
2-19
Chapter 2 Theory of Operation
PCI E Series RLPM