SBS Technologies 466-1, Руководство по оборудованию

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Model 466-1 Adapter
VMEbus Adapter Card Configuration 25
A priority arbiter provides requesters preferential control of the data transfer
bus over the other levels. By definition, BR3 is the highest priority, and BR0
is the lowest. When two or more requests are pending, the arbiter assigns
control of the bus in the appropriate order by granting the bus in this sequence.
The priority arbiter must assert BCLR when a bus master of higher priority
than the one in control of the bus initiates a request. When BBSY is asserted
and a request is pending, the arbiter will drive BCLR if the pending request is
of higher priority than the bus grant of the previous arbitration. Although the
current bus master is not required to relinquish control of the bus in any
prescribed time limit, it can continue transferring data until it reaches an
appropriate stopping point.
A round-robin arbiter gives equal priority to all bus request levels. It grants
control of the bus on a rotating basis. Upon release of the bus, the arbiter steps
one level and tests for an active request and asserts a bus grant. If no request
is active, it continues stepping through the levels until a request is found.
The RRS arbiter can optionally drive BCLR. In RRS mode BCLR is asserted
whenever a master requests the bus on a level other than the last one granted.
It does not assert BCLR if a master on the same level requests the bus.
4.3 VMEbus Adapter Card Factory Settings
VMEbus adapter cards are configured as follows when shipped:
VMEbus Dual Port RAM Range Disabled
VMEbus Remote RAM Disabled
VMEbus Address Bias Pass Through
VMEbus Adapter I/O Range 0x2000 – 0x201F
VMEbus R-INT Jumpers None
VMEbus T-INT Jumpers None
VMEbus IRQ Level Remote IRQ1 and IRQ2
VMEbus Grant/Request Level Bus Requester on Level 3
VMEbus card NOT driving VME SYSCLK
VMEbus card NOT driving VME SYSRESET
VMEbus card NOT driving VME bus timeout (BERR)
The VMEbus adapter card is not the system controller.