User`s guide

54 • Operation Theory
4.5 Trigger Sources
We provide flexible trigger selections in the DAQ/PXI-22XXseries products.
In addition to the internal software trigger, DAQ/PXI-22XX also supports
external analog, digital triggers and SSI triggers. Users can configure the
trigger source by software for A/D and D/A processes individually. Note
that the A/D and the D/A conversion share the same analog trigger.
4.5.1 Software-Trigger
This trigger mode does not need any external trigger source. The trigger
asserts right after you execute the specified function calls to begin the
operation. A/D and D/A processes can receive an individual software
trigger.
4.5.2 External Analog Trigger
The analog trigger circuitry routing is shown in the figure 39. The analog
multiplexer could select either a direct analog i nput from the EXTATRIG pin
(SRC1 in figure 39) on the 68-pin connector CN1 or the input signal of ADC
(SRC2 in figure 39. That is, the first channel input you fill in the Channel
Gain Queue). SRC1 can be used for all trigger modes while SRC2 can only
be us ed for post and delay trigger modes. The range of trigger level for
SRC1 is ±10V and the resolution is 78mV (please refer to Table 14, the
valid code range is from 1 to 255), while the trigger range of SRC2 is the
full-scale range of the first channel input in Channel Gain Queue, and the
resolution is the desired range divided by 256. For example, if the first
channel input in Channel Gain Queue is CH0 with bipolar ±5V range, the
trigger voltage would be 4.96V when the trigger level code is set to 0xFF
while –4.96V when the code is set to 0x01.
AIn
n = 0, ...,63
Instrumentation
Amplifier
A/D
Converter
Input Multipexer CN1
MUX
Analog
Trigger
Circuit EXTATRIG
SRC1
SRC2
Figure 39: Analog trigger block diagram