Eingabeschaltkreis und elektronische Regel- bzw. Steuereinheit, welche mit einem derartigen Eingabeschaltkreis versehen ist

An input circuit commonly uses input ports of a microcomputer for a plurality of contact input terminals such as switches provided on the way to the ground. Transistors (Q 1 ) to (Q 8 ) whose bases are connected with contact input terminals (IN 1 ) to (IN 8 ) are provided. Groups of transistors, such as odd-numbered transistors and even-numbered transistors, are made selectable or non-selectable together by a selection output from an I/O port (P 01 ) or (P 02 ) of a microcomputer ( 12 ), and collector currents of a plurality of transistors (Q 1 , Q 2 ; Q 3 , Q 4 ; Q 5 , Q 6 ; Q 7 , Q 8 ) which are not simultaneously selected are converted into voltages using common resistors (R 1 ) to (R 4 ). These voltages then are fed to I/O ports (P 1 ) to (P 4 ). Accordingly, even upon a rise of a contact input from a ground potential due to the ON resistance of switches (SW 1 ) to (SW 8 ), the states of the contacts can be judged precisely.