Microcomputer with watchdog timer and I/O port control

摘要

In a semiconductor device such as a one-chip microcomputer having therein a runaway monitor (watch dog timer) there is provided a control unit for directly controlling the state of an input/output port on the basis of an output (overflow signal) of the runaway monitor and for controlling, in response to the detection of the runaway, the input/output port so that only the input of the input/output port becomes effective. This arrangement can separate the semiconductor device from an external system at the real time when the semiconductor device enters into the runaway state.