Overview
In 1990, SCPI became defined with the IEEE 488.2 specification. The standard specifies a common syntax, command structure, and data formats, to be used with all instruments. It introduced generic commands (such as CONFigure and MEASure), which could be used with any instrument. These commands are grouped into subsystems. SCPI also defines several classes of instruments. For example, any controllable power supply would implement the same DCPSUPPLY base functionality class. Instrument classes specify which subsystems they implement, as well as any instrument-specific features.
The physical communications link is not defined by SCPI. While originally created for IEEE-488 (GPIB), it can also be used with RS-232, Ethernet, USB, VXIbus, etc.
SCPI commands are ASCII textual strings, which are sent to the instrument over the physical layer (e.g., IEEE-488). Commands are a series of one or more keywords, many of which take parameters. In the specification, keywords are written CONFigure: The entire keyword can be used, or it can be abbreviated to just the uppercase portion. Responses to query commands are typically ASCII strings. However, for bulk data, binary formats can be used.
Read more about this topic: Standard Commands For Programmable Instruments