row without disturbing those already in use. ELECTRONIC In the most usual form of construction, the movement of the bars MARKERS REGISTERS is produced by a slight rotation about the pivot in a manner similar to the armature of a telephone relay. The spring finger is attached to the select bar and swings across when the bar rotates. The function of the register is to receive the caller's instructions ELECTRONIC ELECTRONIC in the form of dialled digits and convert them into the appropriate SCANNER PROCESSORS signals for route selection. Operation of the relevant magnets in the required crossbar switches in the concentration stage (CS) and the group selection stage (GS) is carried out by the markers. Each marker is directly associated with a set of crossbar switches Figure 31.16 Reed electronic exchange which it serves exclusively. The registers are available in a common pool and are assigned as required to incoming calls. The subscriber's line circuit (LC) detects the calling condition and same set of switches and the complete operation of setting up a path signals to the relevant marker which causes CS to connect the is controlled by a processor, which corresponds to an operator and calling line to a free transmission bridge (TB). This in turn cooper- can observe directly the state of the whole exchange. Several pro- ates with another marker to set a connection through the Register cessors are provided per exchange and they work independently of Finder (RF) to seize a free register. one another, as did the operators on a multiple position switchboard, Unlike the Strowger system, the number of switching stages need sharing only common directory information and operating rules. not be related to the exchange numbering scheme. Provided the processors are made powerful enough, the systems organised in this way have again begun to acquire the power and 31.4.4 flexibility associated with an operator-controlled manual exchange. Central control (Reed systems) 31.4.5 Distributed control The use of registers represents one 