LAN eXtensions for Instrumentation (LXI) does more than specify a local-area-network (LAN) interface on a standalone instrument. It was spawned to replace the aging General Purpose Interface Bus (GPIB) as the industry standard for connecting test and measurement equipment. The LXI standard also was developed to specify a complete modular standard with requirements for size, cooling, multi-device synchronization, triggering, and more. The LXI specification describes three classes that must adhere to some subset of the full specification. LeCroy's oscilloscopes are Class C LXI instruments, which gives the company the expertise to explain this specification in an application note titled, "Introducing the LXI Interface."
The six-page document begins by detailing primary LXI features. In terms of the LAN interface, for example, all compliant oscilloscopes include a standard RJ45 connector to link the oscilloscope to a network or PC via a crossover network cable. The LXI LAN interface uses the VXI11 protocol on top of the TCP/IP stack. To automatically detect LAN instruments on the network, the standard demands that instruments support VXI11 discovery. Only enough of the VXI11 protocol has to be implemented to allow discovery as the execution of simple *IDN queries. For further communications with the instrument, manufacturers can switch to their own proprietary protocol.
To comply with LXI, manufacturers also must provide an Interchangeable Virtual Instrument (IVI) driver. This driver provides a standard application programming interface (API) for communications with instruments. As a result, users can potentially interchange instruments without changing their source code. Note that IVI drivers use the Virtual Instrument Software Architecture (VISA). Programmers working with drivers that employ a VISA interface layer usually avoid the need to deal with the low-level details of the communications bus. In terms of a web interface, the LXI specification demands that compliant instruments include a web server that responds to a standard http request to its IP address.
The note closes with a discussion on using LXI features. To automatically find instruments and create aliases, LeCroy recommends the use of National Instruments' Measurement & Automation Explorer (MAX). Overall, this application note offers step-by-step, hands-on information for oscilloscope users who are just getting acquainted with LXI. In doing so, it shows how the interface simplifies remote-control operation.
LeCroy Corp., 700 Chestnut Ridge Rd., Chestnut Ridge, NY 10977-6499; (845) 425-2000, FAX: (845) 578-5985, Internet: www.lecroy.com.
