VAX Q-bus to CAMAC systems crate interface for long CAMAC branches

摘要

The TRIUMF Central Control System (CCS) was to be upgraded to use Q-bus-based VAXs. The CCS consists of multiple computers interfaced to a CAMAC Executive Crate with long parallel branches containing multiple pairs of differential branch extenders (DBE). The Creative Electronics System SCI 2280 systems crate interface used for the Q-bus VAX requires the CAMAC operation to complete synchronously with the Q-bus cycle in less than the Q-bus timeout period. This translates to a maximum branch length of about 150 meters containing three pairs of DBEs, which was not adequate. A Q-bus-to-SCI 2280 interface was built to allow CAMAC cycles to be decoupled, when desired, from the Q-bus cycles. When cycles are decoupled, completion of the CAMAC part can be ascertained by testing flags in the interface. The interface design and operation are described and the results of tests using a VAX 3500 are given.