Abstract :
For synchronising operations in a distributed computer or control system where the units are closely coupled, the three-wire synchroniser, originally developed for the 1987 IEEE Futurebus Standard, has some advantages over the use of common clock waveforms. After pointing out these advantages and reviewing the operation of the synchroniser, the paper presents a recent development in which each unit of the system can carry out several sequences of operations concurrently, the sequences being largely independent of one another. Within any unit, the different sequences will generally operate on the same set of registers, and so precautions have to be taken to prevent operations in two or more of the sequences from accessing the same register at the same time. This is done by arranging for any sequence to be able, when necessary, to cause other sequences to pause, but otherwise each of them proceeds at its own maximum speed.
