Abstract: An electronic circuit board electrically connected to other circuits of a data processing system by means of a bus, may be removed and re-inserted in the system without the necessity of disabling other circuits connected to the bus. A latch actuated switch provides a control signal in anticipation of circuit board removal. The control signal activates a finite state machine which seizes control of the bus after completion of any current bus communications and stops the generation of clock pulses normally required in bus communications. When contact is physically broken between the board and its corresponding connector, the finite state machine restores the bus clock pulses and relinquishes control of the bus. When a board is to be inserted in an open connector, contact between the board and the connector is sensed by the finite state machine which causes the bus to be seized and the bus clock pulses to be temporarily inhibited.