Cross Triggering in WaveForms (Under Construction)

This guide explores the use of cross-triggering between different instruments within WaveForms. Note that there are many applications and approaches to cross triggering beyond what will be covered in this guide.

• A Digilent Test & Measurement Device with Analog I/O and/or Digital I/O
  • Note: Users without a device may still find this guide informative
• A Computer with WaveForms Installed

In the general sense, cross triggering describes systems where multiple instruments - often different devices - share trigger events. This can mean that either both instruments capture the signal containing the trigger event, or that when one of the instruments detects the trigger event, it generates a signal to trigger the other instrument.

This guide demonstrates how to perform cross triggering between multiple WaveForms instruments with a single Digilent Test & Measurement device.

This example demonstrates how using cross triggering makes it easier to change trigger sources across multiple instruments.

If needed, power the Digilent Test and Measurement Device and turn it on, then connect the device to the computer.

Connect the analog input channel 1 positive pin (1+, orange cable) to the waveform generator output channel 1 pin (W1, yellow cable). Then connect the analog input channel 1 negative pin (1-, orange and white cable) to ground (down arrow, black cable). Lastly, connect the external trigger 1 pin (TRIG 1, grey cable) to the digital input/output pin 0 (DIO 0, pink cable).

The circuit achieved by these connections is a simple loopback, allowing the test and measurement device's waveform generator to provide a stimulus for its own oscilloscope, and to generate an external trigger with its digital I/O.

Launch WaveForms, then open the following instruments and apply the following changes to their settings:

1. Open a new Wavegen instrument.
   • Set the Channel Synchronization to Independent
   • Set the Trigger source to Manual
   • Set the Wait time to none
   • Set the Run time to 1 ms
   • Set the Repeat count to infinite
   • Leave all other settings as their defaults
2. Open a new Scope instrument.
   • Set the Trigger Mode to Repeated and Normal
   • Set the Trigger Source to Wavegen 1
   • Set the Time Position to 0 s
   • Set the Time Base to 1 ms/div
   • Disable Channel 2 by unchecking its box
   • Leave all other settings as their defaults
3. Open a new StaticIO instrument.
   • Configure DIO 0 to be a button that outputs 0 when released, and 1 when pressed

More information on how to use each of the instruments used in this example can be found in their respective “Using the …” guides, linked above.

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Now that the workspace and hardware are set up, experimentation with the resulting system can begin.

Click the Wavegen and Scope instruments' Run () buttons. The instruments' states will go from Ready to Armed, meaning that each is now waiting for a trigger to occur.

Click the Manual Trigger button in the bottom left-hand corner of the WaveForms application to trigger the Wavegen instrument to output a signal once. The signal plays back so quickly that the Wavegen's state transition from Armed to Running back to Armed will probably not be seen. The Scope's state will go from Armed to Trig'd back to Armed, and the captured event will be displayed in the Scope's plot.

Next, try modifying the Wavegen trigger's Wait time field. Any value will work. Click the Manual Trigger button again. The Scope take another capture. Despite the changes, the captured signal will be placed at the same point in the plot. Modifying the Wavegen trigger's wait time also affects the Scope trigger: both instruments wait for that amount of time after the Manual Trigger to capture/generate the signal.

Next, change the Wavegen trigger's Source field to External 1. In the StaticIO instrument, click the button corresponding to DIO 0. Observe that this button has the same behavior as the Manual Trigger.

In conclusion, note that through each of these changes to the trigger configuration, the Scope trigger did not need to be reconfigured at all!

This example demonstrates a simple approach to comparing data captured using two devices at once

1. Open two instances of WaveForms.

2. Use each WaveForms instance's device manager to connect one device to each instance.

Note: Using docking windows to present all instruments within the same window is highly recommended.

{
  // Create a reference channel to contain the imported acquisition
  var r = Scope.Ref1.Range.value
  var o = Scope.Ref1.Offset.value
  Scope.Ref1.Clone(Scope.Channel1) 
  Scope.Ref1.Range.value = r
  Scope.Ref1.Offset.value = o
  // Open the file exported by the secondary instance
  var f = File("1.bin")
  // Wait for the other instance to finish saving data
  for(var i = 0; i < 1000 && !f.exist(); i++);
  // Read data from the file and save it into the reference channel
  var rg = f.readDouble()
  f.deleteFile()
  Scope.Ref1.data = rg
}

{
  // Create a binary file and write the channel 1 acquisition into it
  var f = File("1.bin")
  f.writeDouble(Scope.Channel1.alldata)
}

Now that the workspaces and hardware are set up, experimentation with the resulting system can begin.

This multi-device system connects the Wavegen and Scope instruments of the two devices together, so that all are triggered by the same external trigger, sourced from the primary device's digital input/output channel 1, which is driven by the StaticIO button.

Using multi-device systems like this allows a user to greatly extend the number of analog signals that can be captured at once. For the Analog Discovery 2, each additional device adds another two analog input and output channels to the overall system, and digital I/O could easily be added as well. While the two captures are not perfectly aligned (each device runs on its own oscillator), the overall system may be good enough for use in some applications.

Managing many devices with the WaveForms application can get clunky. However, WaveForms SDK is available for users that want to develop their own applications, and can readily support a large number of devices.

Especially when using multiple devices, the calibration (or lack thereof) of the devices may affect the ability to compare acquired data. For more information on calibrating your Test and Measurement device, see the Calibrating a Digilent Test & Measurement Device (REDIRECT) guide.

For more guides on how to use the Digilent Test & Measurement Device, return to the device's Resource Center, linked from Instrumentation page of this wiki.

For more information on WaveForms, visit the WaveForms Reference Manual.

For technical support, please visit the Scopes and Instruments section of the Digilent Forums.

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