is selected none of the functions are operative that is each of the function performing means is placed in its non operating state this is accomplished in the circuit of fig3 by arranging the interconnection of relay contacts such that when all four relays are inactivated lines l1 l8 are all open circuits leaving all of the function performing means in their non operative states fig4 is a logic truth table in which the relay combinations for each function are defined in terms of the state of each relay in the combination the left column of the table lists the functions each of the remaining four columns lists the state of one of relays r1 r4 a one state is a relay column indcates that that relay is activated that is its normally open contacts are closed and its normally closed contacts are open a zero state indicates that the relay is not activated that is its normally closed contacts are closed and its normally open contacts are open an x state represents a 34 don 39 t care 34 condition in which the state of that relay has no effect on the corresponding function thus each row represents as a four bit code the combination of activated and non activated relays associated with the function for that row which when selected enables that function to be performed referring now to fig3 and fig4 the operation of the illustrative embodiment of the circuit of this invention will.