INTERFACE CIRCUIT

PROBLEM TO BE SOLVED: To realize an interface which can cope with later design changes. SOLUTION: A switching element 1 acting as a pull-up resistance in an on- state is arranged at the input side of a buffer 2 in the input stage of an interface circuit, as shown by a figure (a). A control signal S is applied from the outside to a control terminal (gate terminal in the case of an MOS transistor) for turning on/off the switching element 1 to perform the on/off control of the switching element 1. When the switching element 1 is controlled into an on state with the control signal S, a state in which the pull-up resistance is connected can be obtained, and when the switching element 1 is controlled into an off state, a state that the pull-up resistance is not connected can be obtained. Thus, the interface is made compatible even with the later design changes, this situation applies also to a pull-down resistance shown in a figure (b).