Patent ID: 6859898

Claim:
A monitor apparatus for a sequential-function-chart-type programmable controller, comprising: a reference-active-time memory unit configured to store a standard value of an active time of an arbitrary step in a sequential-function-chart program; a timer configured to measure actual active time of the arbitrary step; an anomalous-state monitoring unit configured to detect an anomalous state of the arbitrary step through a comparison between the active time measured by the timer and the standard value stored in the reference-active-time memory unit; a display unit configured to display the sequential-function-chart program steps in such a manner that a step which has been detected by the anomalous-state monitoring unit to be in an anomalous state is distinguished from other displayed steps; and an execution monitor unit configured to store data indicating whether or not each step in the sequential-function-chart program has been executed, wherein the display unit is further configured to display the sequential-function-chart program steps in such a manner that any step or steps which have been executed are distinguished from any step or steps which have not yet been executed, on the basis of the data stored in the execution monitor unit so as to indicate a history or path up to the step detected to be in an anomalous state, wherein the history or path up to the step detected to be in an anomalous state is reset by eliminating data indicating executed steps from the data stored in the execution monitor unit during an initial step of the sequential-function-chart program.