Backup support gives vmebus powerful multiprocessing architecture
C. Mackenna, R. Main, J.A. Black · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 1984
The VME specification-a joint effect of Mostek, Motorola, and Signetics/Philips-now defines three separate buses: the vmebus, the vmxbus, and the vmsbus. Each may be used independently of the others or all three may be used to produce a highly capable multiprocessor system architecture. The vmebus provides parallel nonmultiplexed 8- and 16-bit data and 16- and 24-bit addressing paths on a single connector. It can be increased to full 32-bit data and addressing by using part of a second card connector. The seven interrupt lines and four arbitration lines can be configured according to design requirements. The vmxbus uses the balance of the second connector to provide another parallel path for data transfer and addressing. Unlike the other two buses, the vmsbus uses message frames on a self-arbitrating serial bus to pass messages among functional modules within a backplane or in separate card racks. Together, these three buses can be combined to maximize multiprocessor throughput.