VME (VITA 1) An open system architecture of real-time modular embedded computing systems

The VMEbus specifications continues to evolve as the VMEbus community innovates and finds new approaches to achieving better performance and throughput. The VMEbus specification utilizes IEC and IEEE standards. The VITA Standards Organization enables members to discuss, plan and develop standards.

VME is an asynchronous open standard architecture designed to be microprocessor independent. VMEbus was implemented as a reliable mechanical standard to enable multiple vendors' boards to be compatible. VMEbus modules (cards/boards) are plugged into a backplane. VMEbus Systems and boards are available in 3U (single height), 6U (double height) or 9U (triple height) sizes. VME provides a more ruggedized system interconnection solution than other bus architectures like PCI.

This architecture enables multiple masters to exist on the bus together and transfer data to slave modules. In order to transfer the data, each master must gain control of the bus using central arbitration which is handled by the system controller. VME includes four sub-busses called the Data Transfer Bus, the Data Transfer Arbitration Bus, Priority Interrupt Bus and the Utility Bus.

VMEbus is considered a hybrid bus because the bus provides for both multiplexed and non-multiplexed signals. VME or VME32 establishes a framework for 8, 16 or 32 bit parallel-bus computer architectures which are non-multiplexed. VME64 adds support for 64-bit and block transfer cycles which reduce overhead by enabling multiple data phases to be transferred within one transaction. Using 64-bit block transfers, VMEbus can transfer data in excess of 80 MBps. Additional standards have been implemented over the years to adapt and extend VME as performance measurements and the industry have required including VME64x, 2eSST (VME320), 2eVME, VXS (VITA 41) and VPX (VITA 46).