Versa Module Europa (VME) Bus

VME bus (Versa Module Europa) is an open-ended, flexible computer backplane bus with a 32-bit wide data path, built upon the Eurocard standard (typical card sizes are 160 x 216 mm and 160 x 100 mm). The VMEbus specification was introduced by Motorola, Phillips, Thompson, and Mostek in 1981, itself having been based on an earlier Versa bus used by Motorola in the 1970s and a distributed arbitration scheme that was basically DEC s Unibus scheme altered to avoid DEC s patents. VME is defined by the IEEE 1014-1987 standard.

The VME bus architecture is comprised of four sub-buses: the Data Transfer Bus, the Arbitration Bus, the Priority Interrupt Bus and the Utility Bus.

Before the coming of CompactPCI technology, VME reigned supreme in the worlds of high-end telecom, military, industrial, and other real-time computing systems. VME has a huge installed base. VME uses a completely memory mapped scheme, and every device can be viewed as an address, or block of addresses. Addresses and data are not multiplexed it s an asynchronous bus, so data can be transferred to each board at its own optimum speed. A typical transfer consists of an arbitration cycle (to gain bus control), an address cycle (to select the register) and the actual data cycle. Read, write, modify and block transfers are supported.

Since it s been around for so long, VME supports a huge number of protocols which allows newer, faster products to be added to a system while at the same...