VXI - VME Extension for Instrumentation
The VME Extension for Instrumentation bus (VXIbus) was a very common bus system in industrial measurement technology. The VXIbus is a modified version of the well-known VME bus, modified for measurement technology. It was originally developed for the Motorola 68000 processor series. As opposed to the VME bus, the VXIbus has dynamic addressing capabilities with manual address and interrupt allocation. This is meant to avoid failures caused by double addressing. This concept was later also implemented for PCs with the transition from the ISA to the PCI bus.
The Persormance data of the VXI bus are as follows:
- 32 bit address bus width
- Data transfer clock of up to 16 MHz
- Up to 256 devices addressable on one bus
- Multi-master-capability, meaning that several master devices can be simultaneoulsy operated on one bus
It is thereby possible to run very fast and comprehensive industrial test systems as well as real-time applications with the VXI bus.
The VXI bus is and has been in competition with the GPIB bus (General Purpose Interface Bus, IEEE-488), which was already developed in the 1970ies, and GPIB bus compatible stand-alone devices like oscilloscopes, function generators, programmable power supplies or digital multimeters were implemented as VXI bus modules. In addition to enhancements regarding the electrical signal variety, the number of available module sizes was also enlarged. Due to the addition of the "C" and "D" size formats, it was possible to fit complex measurement instruments into one slot.
The most popular and most common frame size is the "C" format. The module width for VXI devices was changed to 1.2", facilitating the use of shielded housings and housing-internal shielding panels and reducing the danger of influences by electrical disturbances.
The bus continues to exist in its current version 4, which was introduced in 2010, despite having been discontinued and renewed several times. However, manufacturers have stopped the development of new products some time ago and increasingly discontinue the production and support of available cards. Therefore, since 2014, the era of the VXI bus now really seems to be ending. Still, there are VXI systems running to this day. However, the problem of obtaining spare parts forces users to migrate to the newer, easily globally obtainable system platforms like LXI and PXI.