Screw terminal barrier block for logic & Load connections, Resident pull-up resistors, 5 amp field-replaceable fuses(LITTLEFUSE #251005 or equivalent), LEDs indicate logic status, All even-numbered logic connections are logic ground, Input and output modules accepted interchangeably, Operate with 5, 15 or 24 volt logic supplies, Captive-screw retaining system for C4 Modules