PXI tutorial includes:
What is PXI?PXI standardPXI chassisPXI bus and backplanePXI controllerPXI cards & modulesPXI softwarePXI ExpressPXImc MultiComputingSet-up & build PXI system

The PXI chassis literally provides the framework for the system and it normally can range in size from four slots up to eighteen. The PXI chassis contains a high performance backplane enabling the cards in the system to be able to communicate rapidly with one another and in addition to this timing and triggering lines are also included. Verify that the PXI trigger lines, mentioned in the above step, are reserved, so that no other device can use them. If you are using a System Timing Slot controller to resynchronize the Exported Sync Pulse from the master device, and send it back to all the devices as the Sync Pulse, configure the routing for the PXI trigger line with the Sync. National Instruments has released two additional PXI Express chassis for automated test and control applications. The NI PXIe-1078 nine-slot and NI PXIe-1071 four-slot chassis can be used with PXI Express modules and controllers with the flexibility of backward compatibility with existing PXI modules. PXIe, 18-Slot (16 Hybrid Slots, 1 PXI Express System Timing Slot), Up to 24 GB/s PXI Chassis —The PXIe‑1085 features a high-bandwidth, all-hybrid backplane to meet a wide range of high-performance test and measurement application needs.

The PXI chassis provides the means by which the whole PXI test system is able to be held together. It provides the services which the individual cards require for the operation. It also provides everything from the mechanical card holders to the power supply and the air cooling required in such a densely packed volume.

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The chassis is standardised so that PXI cards and instruments will not only be able to mechanically fit, but electrically operate to their potential within the chassis.

In order to be able to operate correctly, both cards or test instruments and the PXI chassis must conform to the standard. There are a number of salient features within the specification that enable the cards and the chassis to operate together.

PXI chassis environmental requirements

The PXI specifications states that any chassis that are manufactured should be well suited to harsh environments. Although they are not expected to meet the same requirements as military grade equipment, they should nevertheless be able to operate within many industrial environments. For example it may be necessary to operate a PXI chassis in a factory environment for data acquisition where temperatures may vary beyond those seen in a laboratory or where there is some degree of dirty. Certain levels of vibration may also be seen.

To meet these requirements the PXI chassis is based around the Eurocard packaging system used by compactPCI. As part of the system, high performance IEC connectors are used to ensure reliability over long periods of time.

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To ensure that the chassis and its associated modules can operate over a sufficiently wide temperature range, the PXI specification includes specific cooling and environmental requirements. These ensure it is able to operate within a variety of industrial environments.

PXI chassis connector system

The connector system used is crucial to its operation. Connectors can be a considerable source of problems, especially when systems are used within non-laboratory environments. Intermittent contacts caused from poor connectors can be particularly time-consuming to fault find. Accordingly a high reliability connector solution was chosen.

Also to maintain compatibility, PXI uses the same pin-in-socket connector system that is found in the CompactPCI racks and systems.

The connectors used in the PXI chassis are defined by the International Electrotechnical Commission, IEC-1076 and offer a high level of performance under all conditions. The connectors pins are on a 2 mm pitch and are also impedance matched so that they provide a high level of performance within the chassis and are able to provide PXI systems more slots on a single bus segment than traditional desktop PCs systems.

Basic PXI chassis parameters

The chassis system is based around the Eurocard packaging system. This provides a number of advantages including a system that is already established. Furthermore the connectors that are used are the IEC-1076 style. The pins are on a 2 mm pitch giving a very dense connection system. In addition to this they are impedance matched to provide the required performance at high frequencies.

The PXI system supports the two sizes, namely 3U and 6U with the details outlined in the table below:

PXI card sizes
Measurements in mm Measurements in inches
3U 100 by 160 3.94 by 6.3
6U 233.35 by 160 9.19 by 6.3

The 3U standard has two interface connectors. One carries the signals required for the 32-bit PCI local bus and the other carries the signals for 64-bit PCI transfers and the signals for implementing various electrical features of the system. The 6U form factor defines modules that may carry up to two additional connectors for future expansion of the PXI specification. The larger card size also allows for a additional circuitry that may be required for some instruments.

In general the 3U PXI chassis and modules are more widely used. However the 3U modules can be fitted into a 6U chassis using a simple adaptor.

PXI chassis widths

PXI chassis come in a number of different sizes and the correct chassis size or type can be chosen for a given application. There is no need to buy a large chassis at extra cost if only a small number of cards are to be used.

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Generally there are two sizes of chasses - a full 19 inch rack compatible size and a half rack width.

The full rack width chassis typically has 18 slots, whilst the half sized chassis has 8 slots.

PXI chassis slots functions

Each PXI chassis has a number of slots. As mentioned above the chassis have either eight or eighteen slots. Not all the slots can be used for all cards. There are some positions reserved for particular applications.

  • Slot 1: Slot 1 in the PXI chassis is reserved for the controller - this is the only position in which the controller will operate. Normally this is 4 units wide to allow for all the space required for embedded controllers, although some controllers could be smaller. Cards that link out to computers to provide the control are often only one module width and therefore in these circumstances blanking plates may be required to cover the empty space.
  • Peripheral slots: These are slots that can be used for the test instruments, etc. There may be some restrictions on the types of module that can be used in terms of PXI, PXIe, etc, but these are indicated by the glyphs on the chassis as described below.
  • Timing slot: On larger chassis a timing slot may be indicated. This can be used for normal peripheral modules, but it is also the one to be used if any timing or synchronising modules are to be used. This slot is on the bridge between the two sides of the chassis and it provides the shortest delay between all the modules in the rack.

As a further note, if large amounts of peer to peer streaming is required, then it is best to place the two modules that will be streaming the data on the same side of the backplane bridge, i.e. on the same side of the timing slot.

PXI chassis glyphs

In order to identify the different types of modules that can be accommodated within a PXI chassis, small identification glyphs are used with each slot to highlight what it can accommodate.

The numbers in the glyphs normally refer to the slot number, but in this instance the explanations are linked to the glyph numbers:

Chassis
  • 1 PXI Express system slot
  • 2 PXI-1 peripheral slot, i.e. the basic PXI before PXIe was introduced.
  • 3 PXI Express hybrid slot - i.e. it will accommodate both PXIe, and the basic PXI
  • 4 PXI Express only peripheral slot
  • 5 PXI Express system timing slot

It can be seen how the PXI chassis identification glyphs are shown and how they indicate the capabilities of each slot.

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How do I use MAX with my PXI chassis?

To configure your PXI system, you must identify each PXI chassis. (PXI Express chassis are automatically identified.) Identifying your chassis enables features such as slot identification, geographic addressing, and trigger routing. MAX automatically detects all PXI chassis connected by National Instruments MXI bridging kits, but cannot detect the PXI chassis model.

For third-party bridging solutions, you must show PXI buses at the PXI system level to see the bus that represents the chassis. Then you must create a chassis for that bus. Refer to PXI System Basics and PXI Bus Basics for more information.

What can I do at the PXI chassis level?

You can identify your PXI chassis type, view and communicate with devices, renumber the chassis, delete the chassis, and reserve triggers in the chassis.

What do you want to do?

Right-click your PXI chassis and select your chassis model in the Identify As» menu. If your chassis model is not listed, select Other... and choose the file that describes your PXI chassis.

Select your PXI Chassis. After you have identified your PXI chassis, the Slot view displays information about each slot in your PXI chassis. To communicate with a PXI device, right-click the PXI device and select Open VISA Session. You should see an interactive session to communicate with your device.

Right-click your PXI chassis and select Renumber.... Enter or select a new chassis number for your PXI chassis. Chassis numbers must be unique in the PXI system.

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You cannot delete a chassis unless you manually created it by identifying a hidden PXI bus as a chassis, or you had previously identified the chassis and then removed the physical connection to it. To delete your PXI chassis, select the PXI chassis and press <Delete>, or right-click the PXI chassis and select Remove Chassis.

Once you identify your PXI chassis, MAX displays the Triggers pane, where you can configure which trigger lines in the chassis should be reserved. Devices with older drivers and third-party devices may require this reservation to prevent modern drivers, like NI-DAQmx, from automatically routing signals on trigger lines used by those devices. For more information about why trigger reservation may be necessary, see What Is Trigger Reservation, and Why Is It Necessary?

Note that in some chassis with multiple trigger buses, such as the NI PXI-1045, reserving a trigger line in one bus does not reserve any lines in the other buses, and signals are not propagated between trigger buses. To propagate signals between buses, National Instruments chassis with multiple trigger buses support routing trigger signals. Without routing, triggers generated in one trigger bus will not be received in any other trigger bus. You can configure trigger routing in the Triggers pane of the chassis, or routes may be configured on unused trigger lines as needed by newer drivers like NI-DAQmx.

To reserve triggers in your PXI chassis, select your PXI chassis. In the Triggers pane, check the box next to each trigger you want to reserve. Click Save in the toolbar to apply your changes. If the triggers you want to reserve are in use, you must reboot your machine for the changes to take effect.

Note MAX does not recognize third-party software or older versions of some National Instruments software. If you are using such software, you must manually verify that none of the trigger lines you selected is in use.

To route triggers in your PXI chassis with multiple trigger buses, select your PXI chassis. In the Triggers pane, if routing is available for the identified chassis, you may select between several possible routes for each trigger line to cause signals to flow from a source bus to the other buses in the chassis. Routing automatically reserves the trigger line in all buses receiving the source signal. If you do not need a trigger line to maintain a specific routing, select the Dynamic route to allow applications and drivers such as NI-DAQmx to configure routes as needed. Click Save in the toolbar to apply your changes. If the destinations of the chosen routes are in use, you must reboot for the changes to take effect.

For more detailed information, see Configuring PXI Triggers and KnowledgeBase 3TJDOND8: Using PXI Timing and Triggering Functionality.

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For a PXI/SCXI combination chassis, such as the PXI-1010 or PXI-1011, you must also configure the chassis for use with NI-DAQ. For NI-DAQmx, right-click Devices and Interfaces»NI-DAQmx Devices and choose Create New NI-DAQmx Device»NI-DAQmx SCXI Chassis. After selecting the appropriate chassis, follow the instructions provided. For traditional NI-DAQ, right-click Devices and Interfaces»Traditional NI-DAQ Devices and choose Add SCXI Chassis..., selecting the appropriate chassis.