INPUT/OUTPUT UNIT 6MB521/4 WITH 14SEP BUS BOARD AND INTEGRATED ISOLATING MODULE FOR INDICATIONS AND COMMANDS WIRED FOR: 6 SWITCH. DEVICES; NOT ISOLATED 32 SINGLE INDICATIONS; ISOLATED 12 ANALOG INPUTS VIA ME/SY FOR DIRECT TRANSDUCER CONNECTION (ME FOR TRANSDUCERS WITH 6XU; 6XJ) 1 - 8 OPTIC INTERFACES WITHOUT MODULES SERIAL LINKS 8 X FIBRE OPTIC LINKS