ELECTRONIC INDUSTRIAL CONTROL APPARATUS AND SYSTEMS FOR PROCESSING DATA BETWEEN CONTROL LOCATIONS AND PLANT OPERATING EQUIPMENT-NAMELY, MULTIPLEXERS, TERMINAL STATIONS, COMMUNICATION STATIONS, MONITORING PANELS, INPUT AND OUTPUT MODULES, ANNUNCIATOR RELAYS, COMPUTER INTERFACE APPARATUS, PARTS THEREOF AND ACCESSORIES COMPRISING PRINTED CIRCUIT BOARDS, FIELD TERMINAL ASSEMBLIES, COMMUNICATIONS LINK CABLES, MISSING MODULE PLUGS AND ENCLOSURES