SCPI, Standard Commands for Programmable Instrumentation
- a tutorial & basics of SCPI, Standard Commands for Programmable Instrumentation a test language for controlling programmable test and measurement devices.
Standard Commands for Programmable Instrumentation, SCPI, often pronounced "skippy" is a standard used for the control of instrumentation.
Standard Commands for Programmable Instrumentation, SCPI, has been available for many years, but its use is increasing as test automation has developed.
The SCPI, Standard Commands for Programmable Instrumentation specifies a "language" that is aimed at being used for controlling test instruments. It provides a common syntax, command structure and data interchange format.
SCPI uses a set of commands that are recognised by the instruments to enable specific actions to be taken. When written, the first three letters are written in uppercase as these are the ones that define the action. For example commands include MEAsure or CONfigure.
As instrument independent commands can be given, e.g. the set-up of a power supply to deliver 12 volts, many commands are instrument independent, thereby often allowing the interchange of instruments without the need for major re-writes of test software.
SCPI does not define the communications link, although it was originally devised with GPIB use in mind. However these days with a much larger variety of interfaces and links available for controlling instrumentation it is widely used with other standards including RS-232, Ethernet, LXI, USB, PXI, VXIbus, etc.
To ease programming and improve test instrument interchangeability, SCPI includes standard command sets for different groups of instruments. For example all DMMs will have many similar measurement capabilities and these can be included as standard commands.
SCPI development & history
The SCPI, Standard Commands for Programmable Instrumentation standard has its roots in GPIB technology.
GPIB was originally introduced at HPIB, Hewlett Packard Interface Bus in the late 1960s. At this time it provided a method for controlling test instrumentation that had not been previously available to this level of sophistication.
The standard became widely used outside Hewlett Packard (now Agilent) and was generally adopted by several standards organisations including IEEE, IEC, etc. and also became known as the General Purpose Interface Bus.
Alongside the acceptance of the GPIB, a need was expressed for a common language or syntax for programming test instrumentation.
To meet this need, SCPI was developed as a standard means of addressing test instrumentation over the IEEE 488 or GPIB as it was known by that time. This was released in the IEEE 488.2 release of the standard that appeared in 1990.
Since its first release, the use of SCPI has been extended so that it can be used over very many test instrumentation interfaces from GPIB to VXI, and LANs to USB.
In order to promote the concept of SCPI, the SCPI Consortium was set up. The aim of the consortium was to develop and maintain a common interface language between computers and test instruments. This would enable industry wide adoption of a common standard.
After the initial work, the SCPI Consortium voted to become part of the IVI Foundation in late 2002 and the IVI Foundation Board of Directors voted to accept the merger in the spring of 2003. This enabled a much larger organisation to be formed to promote test instrumentation communications across the industry. The IVI Foundation aims to promote the development and adoption of standards for programming test instruments, taking its name from IVI meaning Interchangeable Virtual Instruments.
As a result of the merger, the IVI Foundation has assumed control of the SCPI specifications and all on-going work..
By Ian Poole
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