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What is PXI?

 = PCI eXtensions for Instrumentation



Developed in 1997 and launched in 1998, PXI was introduced as an open industry standard to meet the increasing demands of complex instrumentation systems. Today, PXI is governed by the PXI Systems Alliance (PXISA), a group of more than 65 companies chartered to promote the PXI standard, ensure interoperability, and maintain the PXI specification. For more information on the PXISA, including the PXI specification, refer to the PXISA Web site atwww.pxisa.org.

Natioanal Instrumnents named PXI a rugged PC-based platform for measurement and automation systems.


PXI combines PCI electrical-bus features with the modular, Eurocard packaging of CompactPCI and then adds specialized synchronization buses and key software features. PXI is both a high-performance and low-cost deployment platform for applications such as manufacturing test, military and aerospace, machine monitoring, automotive, and industrial test. 

Integral parts of PXI   

  As defined by the PXI Hardware Specification, all PXI chassis contain a system controller slot located in the leftmost slot of the chassis (slot 1).

Controller options include remote control from a standard desktop PC or a high-performance embedded control with either a Microsoft operating system (such as Windows 2000/XP/7) or a Real-Time operating system (such as LabVIEW Real-Time).


NI PXI System Controllers

On the PXI platform, NI offers 3 options for interfacing with CPU:embedded controller, remote controller or rack-mount controller.

Embedded controllers bring the processor physically into the PXI chassis, creating a complete system.  These controllers run both standard (Windows, Linux) and real-time operating systems and feature integrated peripherals like ethernet, USB and serial ports.

With PXI remote controllers, you can control PXI systems with standard desktop and laptop PCs. The links are high-throughput and software-transparent. PC control of PXI enables use the latest desktops, servers, and workstations for applications that require the highest-performance processor, high-speed or long-duration streaming to disk, etc. Fiber-optic cabling options are available for long distances (up to 200 m) and electric isolation. PXI remote controllers can also be used to build multichassis PXI systems.

Rack-mount controllers are a high-performance computing option in a convenient 1U form factor.  Additionally, these controllers support RAID configurations, for applications demanding high speed data streaming to disk.

Embedded PXI Chassis types

The chassis provides the rugged and modular packaging for the system. Chassis, ranging in size from 4-slots to 26-slots, are available for all different types of applications – portable, benchtop, and rack mount. Chassis are available with all 3U slots, all 6U slots, or a combination of 3U and 6U slots, and chassis are also available with special features such as DC power supplies and integrated signal conditioning.

The PXI Express Backplane

The chassis contains the high-performance PXI backplane, which includes the PCI bus and timing and triggering buses. These timing and triggering buses enable users to develop systems for applications requiring precise synchronization. PXI is built on the modular and scalable CompactPCI specification and the high-speed PCI bus architecture.

 Modular PC-Based Architecture Provides Flexible Functionality. PXI provides a platform with a breadth of functionality available, including analog and digital I/O, high-speed instrumentation, vision, motion, and various interfaces. More than 1,500 PXI Products from More than 70 Vendors. 


PXI Timing and Synchronization Features 

NI provides timing and synchronization solutions for both PXI and PXI Express chassis. As the latest evolution of the PXI platform, PXI Express is designed to deliver a higher degree of synchronization to measurement I/O devices than PXI-1 while remaining backward compatible. PXI Express maintains the 10 MHz backplane clock as well as the single-ended PXI trigger bus and length-matched PXI star trigger signal provided by the original PXI specification. PXI Express also adds a 100 MHz differential clock and differential star triggers to the backplane to offer increased noise immunity and industry-leading synchronization accuracy (250 ps and 500 ps of module-to-module skew, respectively). NI timing and synchronization modules are designed to take advantage of the advanced timing and triggering technology featured in its PXI and PXI Express chassis.

PXIe-1085 System Architecture

The main advantages of PCI Express are the following:

  • Software compatibility – Don’t have to change the software
  • High throughput (up to > 4 GBytes/s) – serial interconnect
  • Scalable bandwidth
  • Dedicated bandwidth per slot – dedicated to each slot instead of being shared like PXI does
  • Peer-to-peer communication
  • Cards are able to talk to each other and bypass the controller. For example a digitizer talking to a FPGA
  • Long life (20+ years in mainstream market)
  • PCI and PCIe are used in many architectures – PCI has been around for 20 years and for 20 more years – Intel is using this throughout their chipsets
  • PXIe has the same setup of controller, modules, in a chassis.