State machine apparatus and methods for encoding data in serial form and

Abstract

A serial data coding system is described in which a state machine (FIG. 5) is provided having a plurality of branching hierarchies N, N+1 of states each corresponding to a different decoding table. Depending upon each received bit of serial data, the state machine moves through these branching hierarchies of states until states 88 corresponding to valid codes are reached whereupon a valid code is decoded and the state machine reset to the start of that branching hierarchy. If it is desired to move between branching hierarchies, then an internal table selecting word is inserted into the stream of serial data to move the state machine into a table incrementing state 90 where a jump to another branching hierarchy of states may be made. In order to cope with an externally applied switching signal Y/C for switching the state machine between branching hierarchies, the state machine is first moved into one of a plurality of transfer states A, C, D etc. These states are chosen to be distinct from all other states of the state machine within any branching hierarchies so there is no ambiguity as to which state should be adopted after receipt of the externally applied switching signal Y/C.