APPARATUS FOR DETECTING OSCILLATION STOP AND APPARATUS PROCESSING AFTER DETECTING OSCILLATION STOP

摘要

PURPOSE: An apparatus for detecting oscillation stop is provided to output the signal to reset the microcomputer by detecting the oscillation stop of an external clock and to convert it into the internal clock of the microcomputer. CONSTITUTION: An external clock(11) is inputted from the external clock input terminal. A microcomputer(12) is mounted on the semiconductor chip. A noise filter(13) removes the noise of the external clock(11). A upward edge detection circuit(14) detecting the upward edge of the external clock(11) consists of inverters(14a-14c) and a NAND circuit(14d). A downward edge detection circuit(15) detecting the downward edge of the external clock(11) consists of inverters(15a-15c) and a NAND circuit(15e). An AND circuit(16) calculates the conjunction of the outputs of the upward and downward edge detection circuits(14,15), and generates one shot pulse during the detection of the upward and downward edges. CPU(18) is synchronized with the external clock(11) of which the noise is removed by the noise filter(13). A register(19) maintains the oscillation stop detection starting signal. A NOR circuit(21) calculates the non disjunction of the output of an inverter(20) and a stop/standby mode signal. A NAND circuit(22) calculates the non conjunction of the outputs of the AND circuit(16) and the NOR circuit(21).