Instrument Bus Development Trend: Unique Bus Technology

For any instrument that can be hooked up with system-level testing, the bus is an essential unit that carries important functions such as data transmission and control in test equipment and systems. The test and measurement instrument industry developed the first instrument bus standard GPIB from the 1960s, adding a new instrument bus approximately every 10 years, and successively introducing VXI, PXI, and LXI. In recent years, there has been a direct migration from the PC peripheral bus to the instrument bus. USB. The prevalence of bus technology has enabled the instruments to bid farewell to their respective battles, making it possible to build test systems and flexible test systems, which has greatly improved the efficiency and application of electronic testing.

Several existing bus GPIB (General Purpose Interface Bus) GPIB was proposed by HP in the 70s, and then approved as the IEEE488 standard, becoming the first program-controlled universal instrument bus accepted by the industry. Up to 14 devices can be connected simultaneously using the GPIB bus. The maximum cable length is 2 meters. Due to its long history, GPIB has the most extensive hardware and software support. Almost all standalone instruments are equipped with GPIB interfaces. The structure and commands of the GPIB measurement system are simple. There are interface signals and connectors specifically designed for instrument control, with outstanding robustness and reliability. GPIB is suitable for automating existing test equipment, hybrid measurement and control systems, and special-purpose instrument systems. The disadvantage is that it cannot provide synchronization and trigger functions for multiple instruments, and the bandwidth is insufficient when transmitting large amounts of data. Due to its long history, GPIB bus is still active in the market.

VXI (VMEbus eXtensions for Instrumentation) Bus The VXIbus Consortium was established in 1987. The VXIbus specification was approved by the IEEE Bureau of Standards as the IEEE-1155-1992 standard on September 17, 1992. The advent of the VXI bus brings advanced measurement and test applications to the modular field. It has a stable power supply, powerful cooling capabilities and strict RFI/EMI shielding. With compact structure, high data throughput capability (the latest 3.0 specification bus bandwidth is increased to 160Mbit/s), accurate timing and synchronization, it is suitable for building large and medium-scale automatic measurement systems and applications with high speed and accuracy requirements. occasion. A single VXI card box can expand up to 13 slots. VXI is now mainly used in large-scale ATE systems, aviation, aerospace and other defense industry.

The PXI Bus PXISA (PXI System Alliance), headed by National Instruments Corporation, was established in September 1997. At the same time PXISA was born, it announced the PXI bus standard version 1.0 and demonstrated the first simple configuration of the PXI instrument. Currently, PXI has been widely accepted and has grown rapidly at an average annual rate of 20%, becoming the future leader in bus technology. The details of the PXI bus will be described in detail in another article.

LXI Bus The LXI bus complex led by Agilent Inc. was established in September 2004. In 2005, the LXI standard 1.0 was released and the first LXI modules were introduced. The infrastructure of the LXI bus is Ethernet, and the global networking of the instrument system from local to wide area is achieved through high-speed Ethernet. The IEEE 1588 accurate timing protocol is used to obtain the global timing synchronization of the entire instrument system. The goal is to build a new generation of test and measurement systems with simple, economical, high-speed, and practical hardware and software, replacing the IEEE 488 (or GPIB) bus that has been in use for four decades. Because both the test and measurement instrument industry and the end-users have experienced use of the Internet, there is no objection to the use of Ethernet as a network carrier. However, there is doubt about the software timing synchronization of the IEEE1588 protocol because the GPIB, VXI, and PXI buses commonly used in the test and measurement instrument industry use hard-wired interconnections of cables and microstrip lines to obtain accurate and extremely short timing synchronization and delay.

USB Bus USB (Universal Serial Bus) As a peripheral bus for PCs, thanks to serial transmission, plug and play, hot swappable, easy configuration, simple cables and connectors, and both DC power supply and transmission rate It is widely used due to its advantages of up to 480Mb/s and price popularity. The VXI and PXI buses of the test and measurement instrument are all extended by the use of a computer's universal peripheral bus. Because this type of bus has a wide range of applications and high performance-to-price ratio, it can be applied to an instrument application with a multiplier effect. The goal of the VXI, PXI bus is to implement a communication network consisting of modular instruments that are not advantageous for use on a single instrument. In a single test instrument, USB has been approved by vendors and users, and the PC peripheral bus is used directly as the instrument bus. The USB bus features are still improving. First, the Wireless USB (WUSB) standard has been adopted, which will enable the interconnection of cableless instruments. Second, the USB supply current will be increased from 100 mA to 2 A for greater power consumption. The power supply of the instrument; third is to increase the transmission rate and speed up the data exchange capability of the storage media. Obviously, USB bus instruments will expand the application range in small and medium test and measurement instruments.

AXIe Bus In November 2009, Agilent Technologies, Inc., Affus, and Test Evolution co-founded the AXIe Alliance, and in June 2010 released the AXIe 1.0 Foundation Architecture Standard and AXIe 3.1 Semiconductor Test Extension Technology. About AXIe bus, another article is introduced in detail.

Development Trends In recent days, Agilent’s high-profile announcement will fully enter into the modular field, and will introduce 48 modular products at one time, including 3 new AXIe bus-based products and 45 PXI bus products. The addition of Agilent will undoubtedly bring considerable impact to the modular test market. On the one hand, it will greatly accelerate the promotion of modular products in the market, and on the other hand, it will pose a great threat to the existing manufacturers in many modular markets. . Regardless, Agilent's joining from one side also shows that modularity has become an important trend in the future development of test technology, and the core of modular technology is a variety of high-speed, reliable and powerful bus technologies.

Any kind of bus has its unique advantages in the industry, and no bus will be perfect enough to replace any other bus. Therefore, the future bus market will not be simply who replaces who. Even the AXIe bus, which is known to be compatible with both the PXI and LXI busses, does not expect it to be unified. In response to the needs of technology, current test instruments and systems are often used to support multiple buses to take advantage of their respective buses, especially in increasingly complex synthetic instrument (SI) systems. From an engineer's point of view, when designing a test system, it is often necessary to balance a number of factors. Today's products are becoming more and more complex, and the requirements for mixed-signal testing are getting higher and higher. This requires the use of the advantages of different bus test platforms to build a mixed test system to meet the test requirements.