Defining Trigger Signal Routes Between PXI Express Chassis With Timing and Synchronization Upgrade

Updated Jan 3, 2024



  • PXIe-1095
  • PXIe-1092
  • PXIe-1084


  • LabVIEW


  • PXI Platform Services
  • NI-DAQmx

Operating System

  • Windows

Programming Language

  • LabVIEW G


  • HDMI Cable for Trigger Routing(or High-Density Trigger cables)
  • PXI Timing and Synchronization Upgrade

This article will explain and walk through how to configure triggers between multiple PXIe chassis which are connected together with MXI connection and through the Timing and Synchronization(T&S) Upgrade, what all of the chassis have.

1. PXIe Chassis Front Connections

Disclaimer: The remote chassis does not necessarily need to be MXI’ed into a system. This is why the article does not describe the configuration of the MXI connection. If you need help regarding the setting up of the MXI connection, please refer to the MXI hardware's manual or refer to the MXI-Express Compatibility and Connectivity Troubleshooting Guide.

Currently, only the PXIe-1095, PXIe-1092, and PXIe-1084 chassis have the option to be purchased with a Timing and Synchronization Upgrade. This optional upgrade provides inter-chassis trigger routing capability, higher accuracy CLK10, and CLK100, connectors for 10 MHz reference clock input and output, and remote chassis monitoring and inhibit control.

2. PXIe Chassis Rear Connections
  • PXI Platform Services18.1 or later is required for OCXO, remote inhibit, and inter-chassis triggering functionality.
  • Many driver APIs support the trigger routing functionality like the NI-DAQmx API, to programmatically configure routes, pleas install a development environment with the driver such as LabVIEW or LabWindows/CVI.
For the best functionality and experience, please always use the most up-to-date version of the software components.

Setting Up the Timing & Synchronization Upgrade Hardware


To connect the chassis PXI trigger lines through the I/O ports on the rear of the chassis you need to use HDMI cables.

3. High-Density Trigger Ports on the Rear of the PXIe Chassis

Off-the-shelf cables may be used to connect adjacent chassis. However, since these cables may be of varying quality, for best performance use NI recommended cables:
  • HDMI Cable for Trigger Routing, 1m (Part Number: 148864-01)
  • HDMI Cable for Trigger Routing, 2m (Part Number: 148864-02)
This allows you to send trigger signals to, and receive trigger signals from, devices in other chassis.


If we take a look at the labeling of the HDMI connectors we can see that there are two names associated with each connector.

4.HDMI Connector Labeling
This is due to the combined functionality of the trigger signal sharing and the 10MHz reference clock synchronization through the HDMI cables. This can be observed in the pinout table of the HDMI cable, yellow marks the trigger lines green the in and out pins of the 10MHz reference clock.
To start daisy-chaining your PXI systems through the T&S Upgrade the recommended connection is the Chassis 1 Port 1 to the Chassis 2 Port0 (it is possible to connect the Chassis 1 Port 0 to the Port 1 of Chassis 2 but in this case, the Cassis 2 will be the 10MHz reference clock source). The trigger ports require that they connect to the opposite port on a remote chassis.

6. Valid Port Combinations
To connect Chassis N+1 into the chain, connect Chassis N's free port to the opposite port of Chassis N+1. For example, if the free port on Chassis N is Port 1 then connect it to Chassis N+1 Port 0, if Port 0 is free on Chassis N then connect it to Port 1 on Chassis N+1. Repeat this for any number of chassis.

Additional useful information

  • The cables are "hot-pluggable", changes in how they are connected are comprehended in real-time, and this should be reflected in NI-MAX.
  • Every line is bidirectional and the trigger signals can go in or out on either port. The “In/Out” indications on the rear can be misleading in this way – they refer only to the 10MHz reference clock signal and have no meaning concerning the trigger lines.

Misuse Cases

  • The system does not detect the invalid configurations, and so it will appear to the user that no chassis connect on the remote end of the cable, no damage will occur.
  • Connecting chassis in a "circle" is not supported, but no damage will occur, measurements may be inaccurate or cards may not operate properly.
  • Connecting a single chassis with an HDMI cable in a "loop-back" fashion (Chassis 1 Port 0 to Port 1) is not supported, but no damage will occur, measurements may be inaccurate or cards may not operate properly.

Configuring Trigger Routes with Software

Disclaimer: To be able to configure routes in LabVIEW you will need to install the NI-DAQmx driver .

Confirming Operation

With PXI Platform Services version 20.0, the T&S Upgrade will show up in NI-MAX with the following indicators when selecting the chassis:

  • The Internal Oscillator is OXCO
  • Visible TRIG/10MHz Port 0 Status and TRIG/10MHz Port 1 Status


7. T&S Upgrade Indicators in NI-MAX

Another way to confirm that the extension is working is the following:

  1. Open LabVIEW.
  2. Create a new VI.
  3. Open the Block Diagram.
  4. On the Functions Palette go to Measure I/O>>NI DAQmx>>Advanced>>Signal Routing
  5. Place a DAQmx Connect Terminals VI on the block diagram.
  6. Create constants for the Source Terminal.
  7. Click on the drop-down menu of the terminal.
  8. Find the PFI ports of the extensions for all of your chassis.

8. PFI Ports of the T&S Upgrade in LabVIEW

In the dropdown menu for the NI Terminal type, the DSUB PFI ports always show up when a T&S Upgrade is installed. When a chassis connect on the other end of the cable that isn’t part of the host system (i.e. a multi-host system), the “PortX/TrigY” endpoints show up.

9. Trigger Lines in a Multi-Host System

These are hidden when MXI’ed chassis connect (i.e. a single-host system). This is because users are encouraged to route between modules or, when that isn’t possible, between chassis backplanes. Routing infrastructure will determine a path across the cables.

Setting Up Trigger Routes

It is possible to implement the trigger signal routes in different ways. However it is recommended to create a complete route from where a signal originates to where it is consumed, in one step; where that isn’t possible, do it in the fewest, largest portions possible is preferred.

The trigger signal route implementation types are the following based on their lifetime:

Dynamic (a.k.a "Task-Based" or "Session-Based") - Dynamic reservation/routing/deallocation is on the fly within a user program based upon National Instruments APIs such as NI-DAQmx. Route or Reservation(R&R) is scoped to the lifetime of the process or session used to create it. When the program or session closes, the R&Rs are undone as well.  Example: Trigger routes created with the DAQmx Trigger VI are deleted with the cleaning up of their DAQmx tasks.

Static -  Static reservation pre-allocates a trigger line to prevent its configuration by a user program. This R&R stick around permanently, even past system reboots, until the user deliberately does something to undo them. Example: Trigger routes created in the PXI Trigger Pane in MAX.

The T&S Upgrade supports only dynamic trigger route implementation:


"National Instruments drivers such as NI-DAQmx must be used to route triggers between chassis dynamically; routing triggers between chassis using static routes defined in MAX is not supported."
10. Quote From the
Manual of the PXIe-1095

If possible use dynamic routes, this is because the dynamic route declaration binds the route to the operation that’s leveraging it, providing the best usability and maximizing our ability to manage routing resources automatically, including cleaning them up.


As a first step, make sure that the trigger settings of the PXI chassis are set to "Dynamic" for all the trigger busses that you are intending to use for cross chassis triggering. You can set this in NI-MAX by clicking on the PXI chassis and locating the Triggers tab on the bottom of the window. With this the routes are left unconfigured and available for National Instruments products to perform programmatic or automated routes to connect devices.


11. PXI Chassis Trigger Settings

Some NI drivers support implicit trigger routings, like NI-DAQmxNI-DCPower, and NI-XNET (to see if your driver supports automatic route creation, please refer to the specific driver Help documentation).

Implicit - A concrete trigger source can be specified from different hardware/card which also can be in a different chassis. Example: The start trigger of the analog input on the DAQmx card (Dev1/ai/StartTrigger) can be configured for the trigger source in the "input terminal" of the DCPower Configure Trigger VI.

This is always supported for the above-mentioned drivers, including the case when the T&S Upgrade is used:


12. Dynamic Trigger Route Creation With Implicit Declaration

Many other drivers that are commonly used like NI-DMM, NI-RFSA, NI-RFSG, etc. use explicit trigger routing.

Explicit - The device can only specify the PXI trigger bus line to export or import a trigger signal to or from. Example: The NI-RFSG Export Signal VI can only specify the PXI_Trig0 line for trigger signal exportation.

The PXI trigger bus naming can differ for some of the drivers when using the trigger configuration VI, for example, PXI_Trig0, TTL0, RTSI 0, but all of them refer to the same PXI trigger lines from 0 to 7.


13. Trigger Configuration VI

When working with these drivers, it is possible to implement them in a dynamic route fashion with the help of the DAQmx Connect Terminals VI. This is needed since the majority of the drivers can only specify the PXI trigger bus to listen on for a trigger signal and cannot refer to a specific signal on a specific device, as seen before in case of the DAQmx, DCPower and XNET.

To connect together the intermediate connections between the PXI trigger busses, which were defined for the drivers, the DAQmx Connect Terminals VI should be used. In this case too, the cards can be in different chassis.

14. Partially Specified Route With DAQmx Connect Terminals VI

The defined terminals are connected together automatically by the DAQmx driver, so the programmer does not have to define each subpart of the signal path but this connection also has to be disconnected programmatically with the DAQmx Disconnect Terminal VI at the end of the measurement session.

15. Disconnecting Trigger Route With DAQmx Disconnect Terminal VI


As we can see it depends on our situation, like what drivers are we using, and if our hardware is a multi-chassis system, we need to use different approaches to route our trigger signals.
  1. The most important, when setting up the cabling, is to have a clear understanding of where the 10MHz reference clock originates if possible follow the recommended Port connection order in the Connections section.
  2. Use the DAQmx Connect Terminals VI/DAQmx Disconnect Terminals VI in the case of the drivers which does not support Implicit signal routing.