VME and VXI bus interfaces and adapters allow VME buses and VXI buses to communicate with other types of computer systems and devices. Buses are data connections between computers and internal or external devices. Bus interfaces and adapters connect peripherals to computers that do not provide native support for a peripheral’s interface. The VersaModule Eurocard (VME) bus is a popular, 32-bit bus used in many industrial, commercial and military applications. It is based on the VME standard, which defines mechanical specifications such as board dimensions, connector specifications, and enclosure characteristics, as well as the electronic specifications for sub-bus structures, signal functions, timing, signal voltage levels, and master/slave configurations. VME extensions for instrumentation (VXI) is an electrical and mechanical standard used mainly with automatic test equipment (ATE). VXI allows equipment from different vendors to work together in a common control and packaging environment.

Selecting VME and VXI bus interfaces and adapters requires an analysis of available technologies. The original VME bus (VMEbus) uses Eurocards, rugged circuit boards that provide a 96-pin plug instead of an edge connector for durability. VME64 is an expanded version of the VMEbus that provides 64-bit data transfers and addressing. VME64 is a mechanical and electrical superset of the original VME specification, IEEE 1014 1987, from the Institute of Electrical and Electronics Engineers (IEEE). VME64 features include asynchronous data transfers, an addressing range between 16 and 40 bits, data path widths between 8 and 64 bits, and a bandwidth of 80 Mbps. VME64 extended (VME64x) is an improved version of the original VMEbus that features a 160-pin connector family, 3.3 V power supply pins, bandwidths up to 160 Mbps, injector/ejector locking handles, and hot swap capability. VME160 transfers data at 160 Mbps. VME320 transfers data at a rate of 320 Mbps. VXI combines VMEbus specifications with features from the general-purpose interface bus (GPIB) to meet the needs of instrumentation applications.

There are several form factors for VME and VXI bus interfaces and adapters. A computer board's form factor describes its shape and physical layout. It also determines the types of cases that can be used to contain the board, and the type of power supplies that can be used. The original VMEbus specification recognizes two types of cards: 3U and 6U.  3U cards, also known as single height boards, are 100 mm x 160 mm with one 96 pin DIN connector (J1 connector) on the rear that plugs into the backplane. 6U cards, also known as double height boards, are 233 mm x 160 mm with a second 96 pin DIN connector (J2 connector). For VXI systems, cards are lettered from A to D. Size A cards are 100 mm (3U) x 160 mm. Size B cards are 233 mm (6U) x 160 mm. Size C cards are 233 mm (6U) x 340 mm. Size D cards are 360 mm (9U) x 340 mm. VXI cards with a height of 360 mm (9U) and a length of 400 mm are also available.

VME and VXI bus interfaces and adapters differ in terms of specifications, operating system support, and interfaces to other buses. Specifications include number of ports, transfer rate, random access memory type (RAM), and read-only memory (ROM) type.  Some VME and VXI bus interfaces and adapters are hot swappable. Others conform to requirements from the U.S. Federal Communications Commission (FCC) or feature CE Marking. Support for both proprietary and open-source operating systems is commonly available. Many VME and VXI bus interfaces and adapters are used with CANbus, DeviceNet, Ethernet, and small computer system interface (SCSI) products.