SIGNAL INPUT/OUTPUT CIRCUIT

摘要

PROBLEM TO BE SOLVED: To prevent the data input/output terminals of a single-chip microcomputer which has built-in data input/output function from entering a floating state. SOLUTION: At the time of initialization, an N channel field effect transistor 12 is turned ON by a D type flip-flop 11 and an inverter 10 so that an input/ output port terminal 4 is pulled down. After the initialization, the D type flip- flop 11 holds the N channel field effect transistor 12 ON unless the voltage at the input/output port terminal 4 changes from a low-level state. When the voltage at the input/output port 4 rises to a high level, the D type flip-flop 11 detects the voltage variation and turns OFF the N channel field effect transistor 12.