Archived: Triggering Modes with the NI 5411 and NI 5431

Publish Date: Feb 07, 2017 | 7 Ratings | 4.14 out of 5 | Print

Overview

This document has been archived and is no longer updated by National Instruments.

The NI 5411 and 5431 instruments provide several types of hardware triggering for controlling your waveform generation. All of the methods described here rely on an external signal to trigger changes in the waveform generation. Triggers may be to used to initiate a waveform generation or to step from one waveform stage to another after the waveform output has begun. Click on this link for more information on waveform staging and sequencing.

This document describes the possible sources for the trigger signal. It also discusses the four triggering modes supported by the arb instruments. Exactly how these triggering modes function depends on whether the instrument is being used in Arb Mode or FG (DDS) Mode.

Table of Contents

  1. Trigger Sources
  2. Modes of Operation
  3. Single Trigger Mode
  4. Continuous Trigger Mode
  5. Stepped Trigger Mode
  6. Burst Trigger Mode

1. Trigger Sources

Trigger sources are selected in software. By default, the software produces an internal trigger signal to initiate a waveform generation or to switch from one waveform stage to the next. You can also use an external trigger signal from one of the following three sources:

1. The EXT_TRIG pin on the digital I/O connector (pin #25)
2. The RTSI trigger lines on the RTSI bus (PCI and ISA boards)
3. TTL trigger lines on the PXI trigger bus on the backplane (PXI boards)

If you need to automatically trigger the waveform generation, use software to generate the triggers. A rising TTL edge is required for triggering from all three external sources.

PCI and ISA boards can be configured to trigger off any of the seven general-purpose RTSI pins, RTSI0 through RTSI6. PXI instruments can trigger from backplane lines TRIG0 through TRIG5 as well as PXI STAR.

NOTE: Any external trigger line signal should remain deasserted (logic low) until after software commands have been executed to initiate the waveform generation. The waveform will not actually be generated until after the trigger signal comes in.

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2. Modes of Operation


The NI 5411/5431 has four triggering modes. These trigger modes are available for both Arb and FG (DDS) generation modes. The behavior of the trigger modes may depend on whether the board is being run in Arb or FG (DDS) mode. The four trigger modes are:

1. Single
2. Continuous
3. Stepped
4. Burst

These four modes are detailed below.

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3. Single Trigger Mode


Single trigger mode is the simplest of the four triggering modes. In this mode, a single trigger signal initiates the waveform generation. Any subsequent pulses on the trigger line are ignored. The waveform defined in the staging list is produced once. All timing except the start of the generation is predefined in the staging list.

Single Trigger with Arb Generation Mode
The following figure illustrates single trigger mode used in conjunction with Arb Mode. There are three stages in this example. The first is a sine wave, the second is a sawtooth, and the third is another sine. After the NI 5411/5431 receives a trigger, the waveform generation starts at the first stage and continues through the last stage. NOTE: The last stage is generated repeatedly until you stop the waveform generation. You can settle to a predefined state (such as 0 V) by setting the last stage to this state.




Single Trigger with FG Generation Mode
After the NI 5411/5431 receives a trigger, the waveform generation starts at the first stage and continues through the last stage. The last stage is generated repeatedly until you stop the waveform generation. Figure 2-9 illustrates a single trigger mode of operation for FG waveform generation mode.


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4. Continuous Trigger Mode


The waveform you define in the staging list is generated continually by repeatedly cycling through the staging list. After a trigger is received, the waveform generation starts at the first stage, continues through the last stage, and loops back to the start of the first stage, continuing until you stop the waveform generation. As with single trigger mode, only one trigger is required to start the waveform generation. The difference is that in single trigger mode, the last stage in the staging list is generated continually rather than cycling back through the whole list.


Continuous Trigger with Arb Generation Mode
The figure below shows continuous trigger mode used with the arb generation mode. There are three stages in the list: a sine, a sawtooth, and another sine.





Continuous Trigger with FG Generation Mode
The following figure shows a continuous trigger mode of operation for FG waveform generation mode.


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5. Stepped Trigger Mode


The single trigger and continuous triggering modes described above respond to only one triggering pulse. Any additional pulses are ignored. Like single trigger and continuous modes, the stepped trigger mode described here waits for a trigger pulse to initiate the waveform generation. However, it also requires additional pulses to cycle through the stages in the staging list.

After the initial start trigger is received, the waveform defined by the first stage is generated. The device then waits for the next trigger signal. On the next trigger, the waveform described by the second stage is generated, and so on. Once the staging list is exhausted, the waveform generation returns to the first stage and continues in a cyclic fashion.

Stepped Trigger Mode with Arb Generation Mode
The figure below shows the stepped trigger mode used in conjunction with the Arb generation mode.





If a trigger is received while a stage is being generated, the trigger is ignored. A trigger is recognized only after the stage has been completely generated. While the device “waits” for a trigger to begin the next stage in the list, it repeatedly generates the first eight samples in the next stage. In the diagram above, these eight repeated sample are shown as small, erratic voltages. You can use the first eight samples of a stage to predefine the settling state after the previous stage has been completed.


Stepped Trigger Mode with FG Generation Mode
When FG generation mode is employed, the stepped trigger mode works just like the burst trigger mode with FG. The burst mode is described below.

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6. Burst Trigger Mode


Like stepped trigger mode, the burst trigger mode requires another trigger pulse to move from one waveform stage to the next. However, each stage is generated repeatedly rather than just a single time. After a particular stage has completed, the board begins generating that stage again unless it has received a trigger pulse to move onto the next stage in the list.

Burst Trigger Mode with Arb Generation Mode
The following figure illustrates the burst trigger mode used in conjunction with the arb generation mode. There are three stages: a sine wave, a sawtooth, and another sine.





The loop information associated with each stage is ignored. The number of loops for each stage is determined by the incoming trigger pulses rather than being predefined in the staging list. An incoming trigger pulse tells the board to move on to the next stage. However, the board will finish producing the buffer in the present stage before moving on to the next one. This is why the waveform changes do not line up exactly with the trigger signals in the above diagram.



Burst Trigger Mode with FG Generation Mode
The diagram below shows the burst trigger mode used with the FG waveform generation mode. NOTE: This behavior is identical to stepped trigger mode used along with FG.





As with all FG operations, switching from stage to stage is phase continuous. When burst triggering is used with arb generation as described above, there is a delay before the trigger produces an effect on output because the current buffer is completed before moving on to the next stage. This is not the case with FG; a trigger is registered immediately to produce a frequency change, whatever the phase state of the wave at that point.

When burst triggering is used with FG, the time instructions in the staging list are ignored. The incoming trigger signals determine when the waveform changes from one frequency to the next, so there is no need to use the predefined frequency durations in the staging list.

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