This standard applies to interface systems used to interconnect both programmable and non programmable electronic measuring apparatus with other apparatus and accessories necessary to assemble instrumentation systems. It applies to the interface of instrumentation systems, or portions of them, in which the: 1) Data exchanged among the interconnected apparatus is digital (as distinct from analog); 2) Number of devices that may be interconnected by one contiguous bus does not exceed 15; 3) Total transmission path lengths over the interconnecting cables does not exceed 20 m; 4) Data rate across the interface on any signal line does not exceed 1 Mb/s.; The basic functional specifications of this standard may be used in digital interface applications which require longer distances, more devices, increased noise immunity, or combinations of these. Different electrical and mechanical specifications may be required (for example, symmetrical circuit configurations, high threshold logic, special connectors, or cable configurations) for these extended applications. This standard may also be applicable to other instrumentation system elements such as processors, stimulus, display, or storage devices, and terminal units found useful in instrumentation systems. It applies generally to laboratory and production test environments which are both electrically quiet and restricted as to physical dimensions (distances between the system components). This standard deals only with the interface characteristics of instrumentation systems to the exclusion of design specifications consideration of radio-interface regulations, performance requirements, and safety requirements of apparatus.