GPIB remains in heavy use (Guest Commentary)
By Murali Ravindran, National Instruments -- Test & Measurement World, 5/15/2008 9:11:00 AM
Many instrument-control bus technologies—with varying bus speeds, latency, connectors, cabling, and prices—have come and gone over the years. GPIB, however, continues to be the dominant instrument-control bus in the industry today. In the first quarter of 2008, more than 80% of new instruments publicly announced by leading test and measurement companies incorporated a GPIB interface. “It just works,” is the top response from engineers when asked why they use GPIB for instrument control. In the engineering world of unknowns, it is reassuring to know you can count on your GPIB-based systems to function properly.
Despite the emergence of new instrument-control bus technologies, GPIB remains the foundation for instrument-control systems and serves as a critical bridging technology in applications using multiple instrument-control bus options. Instrument vendors recognize the large installed base and have a long-standing commitment to the longevity of GPIB and the ultimate success of your instrument-control applications.
Developed over 35 years ago, GPIB lets engineers and scientists control their instruments from desktop PCs regardless of vendor. The industry has actively advanced the GPIB IEEE 488 standard and technologies—from integrated circuits and interface cards for multiple operating systems to software, firmware, and application programming interfaces (APIs). These collaborative efforts have helped GPIB become a proven, easy-to-use control interface with the following benefits:
• Thousands of GPIB instruments
• Software compatibility with other instrument interfaces (enabled by VISA and SCPI)
• Proven ease of use and familiarity
• Low-latency bus performance (30 µs)
• Good bandwidth performance (up to 1.8 Mbytes/s using IEEE 488 and up to 8 Mbytes/s using HS488)
• Rugged cables and connectors
• Long-distance remote control through fiber-optic and Ethernet extenders
During the past five years, many GPIB products have been updated to include new features, reduce physical size, and enhance capabilities. Some of these new GPIB products and research areas include the following:
• Windows Vista 32-bit/64-bit support
• Intel-based Mac support
• Mac OS X support
• Sparc Solaris 9 and 10 support
• PCI Express GPIB controller
• Hi-Speed USB-to-GPIB high-speed controller
• RoHS-compliant controllers, cables, and integrated circuits
The success of GPIB and its continued use beyond the next decade are largely related to ubiquitous software and instrument driver availability. Software engineers continue to develop drivers for GPIB-based instruments. Today, the NI Instrument Driver Network (www.ni.com/idnet) offers more than 6100 instrument drivers, with nearly 100 new drivers added in 2008.
Bus choices
No single bus or technology has been able to deliver the best performance, simplest ease of use, and lowest cost. GPIB demonstrates a good combination of these elements, but it is not best in all categories. Thus, you should understand the specific instrument-control needs of your application before choosing an instrument-control bus.
Instrument-control bus comparison
|
Bus |
Ideal Bandwidth (Mbytes/s) |
Latency (µs)
|
Distributed Capability (m) |
Setup Time |
Ruggedness |
|
GPIB |
1.8 (488.1) 8 (HS488) |
30 |
20 (fiber-optic extend to 2 km) |
Better |
Best |
|
USB |
60 (Hi-Speed) |
125 (Hi-Speed) |
5 |
Best |
Good |
|
Ethernet/LXI |
12.5 (Fast) 125 (Gigabit) |
1000 (Fast) 1000 (Gigabit) |
85 to 100 |
Good |
Good |
|
Cabled PCI Express |
250 (x1) 4000 (x16) |
0.3 to 0.7 (x1) 0.3 to 0.7 (x16) |
7 |
Better |
Better |
USB, Ethernet/LXI, and Cabled PCI Express each have advantages as instrument-control buses. USB-controlled devices are well suited for portable applications such as datalogging and in-vehicle data acquisition. The cable length, however, is limited to 5 m and the connectors aren’t rugged. Ethernet/LXI lets you create a network of highly distributed instruments that require remote access capabilities across large geographies. But, Ethernet/LXI has higher latency than other instrument-control buses. Additionally, most new Ethernet/LXI instruments come populated with fast Ethernet ports (100BASE-T), as opposed to the faster Gigabit Ethernet ports. That, combined with latency, can cause significant bottlenecks in high-performance applications. Both USB and Ethernet are standard buses in all PCs and thus don’t require the additional hardware and software that GPIB requires.
Cabled PCI Express is an emerging technology that holds promise for a high-bandwidth, low-latency interface for instrument control and data sharing in high-performance applications. Cabled PCI Express solutions for PXI-based applications look promising for a general-purpose, high-performance test and measurement cabled interface.
GPIB remains a dominant industry standard for general-purpose instrument control, and will continue meeting most engineers’ measurement and automation needs. The dependability of GPIB and industry commitment to the large GPIB install base keep GPIB as the de facto standard for PC-based control of stand-alone instruments, which, in turn, helps engineers and managers reduce costs and preserve instrument investments.
Murali Ravindran is a product manager for PXI Remote Controllers at National Instruments. He started his career at NI in 2004 in the Engineering Leadership Program as an applications engineer. Ravindran holds a master’s in electrical engineering and an MBA in entrepreneurship from the University of Oklahoma. Before joining NI, he worked as a research assistant for three years in the Center for the Study of Wireless Electromagnetic Compatibility and as a business intern for a year in a start-up biotech company.
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