PXI interoperability

26 February 2016

When developing a new test system, the PXI platform presents a great option, offering advantages of high-performance test and measurement with a rugged industrial form factor, flexible module configurations, and scalability for size and number of channels. 

PXI chassis provide a single power source and cooling for a selection of plug-in PXI instruments, switching, and control modules. There are multiple sources for PXI chassis and controllers, and thousands of PXI modules available from many different vendors, making it possible to select and combine modules for nearly every conceivable type of test. With additional software, programing engineers are able to create a compact, unique test system for a specific application. However, when engineers make the decision to build a test system based on the PXI platform, how do they ensure the combined multi-vendor chassis, controller, and modules will integrate and work as expected?

Not all PXI chassis, controllers, or modules work together

The fact is, not all PXI chassis, controller and modules are compatible with each other. This is partially due to different PXI interface revisions for mechanical slot spacing, connector placement and pinouts which are based on PCI bus standards. As the PCI standard has evolved, PXI has also evolved taking advantage of a faster serial bus, improved communications, and faster data transfer speeds. When CompactPCI (cPCI) was introduced, the standards committee required PXI hardware and software design changes to integrate the new cPCI standard. The result was PXI products with two versions of PCI interface designs. The original parallel PCI implementation is known as PXI-1. The newer serialise PCIe style is known as PXIe and includes requirements for PXI-1 backward compatibility.  

For backward compatibility of new PXI chassis, with hybrid style slots, it is important to accommodate existing PXI-1 modules. Also, the PXI-1 modules need to be updated by their manufacturer with a new PXI-1 hybrid slot compatible connector.

For the most flexibility, a PXI chassis with many hybrid slots can be used so both PXI-1 hybrid and PXIe style modules can easily be inserted and make necessary connections. If PXI-1 modules with the additional connector are used, select a chassis with PXI-1 slots or ensure the modules can be converted to PXI-1 hybrid modules. For the best system performance, PXIe modules in PXIe chassis can achieve significantly higher throughput, point-to-point messaging and have improved triggering and synchronisation compared to PXI-1. More PXIe style modules will be available in the future.

Paying attention to certain details, such as interface features and specifications, when selecting an external controller, PCI interface, or embedded controller for a PXI system is also important for interoperability. For remote control, a PCIe plug-in adaptor card is installed in the controller (tower, desktop, or laptop PC) and then routed to the PXI chassis. A long cable between the controller and chassis and/or clock jitter can inversely affect high speed PCIe data transfers. Select a PCIe adaptor card optimised for driving long PCIe cables and provides clock isolation with low clock/data jitter for the best communications and data transfers.

For an embedded controller which plugs directly into the PXI chassis, it is important to know that the chassis backplane connectors for PXI -1 style controllers are different than the connectors for PXIe controllers. A PXI-1 controller cannot be used in a PXIe chassis.
 
M9217A PXIe isolated digitiser

The Keysight M9217A PXIe single slot isolated digitiser offers 2 channels of simultaneous sampling with sample rate up to 20MSa/s/channel and 16-bit resolution per channel. The high voltage input channels can measure up to ±256V for high voltage test like the solenoid driver test. Built-in peak voltage protection of up to 400V prevents damage from high transient voltage or spikes. Both channels are isolated supporting differential measurements. The M9217A provides 32MSa/channel, and memory segmentation of up to 1024 records. Multiple trigger types are supported including; PXI trigger bus, PXI Star, external in/out trigger, channel and software trigger.


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