Giga-tronics 58542, Operation & Maintenance Manual

Page: 33 / 252

Operation
Publication 21555, Rev. E, September 2002 2-3
2.3.2 Data Transfer Bus Arbitration
The power meter has VMEbus Mastership capability. When enabled, it sends responses and events as
signals (software interrupts) to its Commander Signal Register. The power meter cannot drive the
interrupt lines.
The power meter is configured as a level 3 requester by the factory. The level 3 Bus Request and Bus
Grant lines (BR3*, BG3IN* and BG3OUT*) are used. The other Bus Grant lines are daisy-chained by
jumpers (See Figure 2-2).
The VMEbus specifications describe three priority schemes: (1) Prioritized, (2) round-robin and (3)
single level. Prioritized arbitration assigns the bus according to a fixed priority scheme where each of
four bus lines has a priority from highest (BR3*) to lowest (BR0*). Round-robin arbitration assigns the
bus on a rotating basis. Single level arbitration accepts requests only on BR3*.
The jumpers must be changed if a different requester level is required. Figure 2-2 will aid in
reconfiguring the power meter to a new level. Refer to the VMEbus specification for more information
on data transfer bus arbitration.
Figure 2-2: Default Bus Arbitration Settings