EXTERNAL INTERFACE CIRCUIT

PROBLEM TO BE SOLVED: To provide an input/output interface which allows a three-wire resistance sensor to be connected.SOLUTION: An external interface circuit comprises: a switch circuit 105 which switches connection between one connection terminal group and the other connection terminal group; voltage/current conversion circuits 101 to 104 which generate currents for first and second external terminals PIOa and PIOb on the basis of voltages at the one connection terminal group; resistance circuits which are connected between the one connection terminal group and the first and second external terminals and control the current supply to external terminals; two detection circuits 107 and 110 which detect voltages at the other connection terminal group; two control signal generation circuits 106 and 109 which output signals corresponding to difference between input signals and detection signals of the detection circuits, to one terminal in the other connection terminal group; and two input signal generation circuits 108 and 111 which generate input signals corresponding to the voltages at the other connection terminal group.SELECTED DRAWING: Figure 2 【課題】３線式の抵抗センサの接続が可能な入出力インターフェースを提供する。【解決手段】外部インターフェース回路は、一方の接続端子群と他方の接続端子群との接続を切り替えるスイッチ回路１０５と、一方の接続端子群の電圧に基づいて第１および第２外部端子ＰＩＯａ、ＰＩＯｂに対する電流を生成する電圧電流変換回路１０１〜１０４と、一方の接続端子群と第１および第２外部端子との間に夫々接続され、外部端子への電流供給を制御する抵抗回路と、他方の接続端子群の電圧を検出する２つの検出回路１０７、１１０と、入力された信号と検出回路の検出信号との差に応じた信号を他方の接続端子群の一つの端子に出力する２つの制御信号生成回路１０６、１０９と、他方の接続端子群の電圧に応じた入力信号を生成する２つの入力信号生成回路１０８、１１１と備える。【選択図】図２