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there are three selector switches on the front of my plc one labeled rn in one position and st in the other. the other is labeled nr,re,and or.the last one is the power switch. does any one know what these other two for. also I am asuming that you require a 25 to 9 pin adaptor for the 6es5 734-1bd20 cable aswell if communicating with your serial port.