Abstract: In a monitor apparatus for a sequential-function-chart-type programmable controller, a standard value of an active time of an arbitrary step in a sequential-function-chart program is stored, and the active time of the arbitrary step is measured during execution of the program. An anomalous state of the arbitrary step is detected through comparison between the measured active time and the reference value. Further, data indicating whether each step in the sequential-function-chart program has been executed are stored. The program is displayed such a manner that an anomalous step, a step or steps which have been executed, and a step or steps which have not yet been executed are distinguished from one another.

Abstract: A sequence block display system used with a programmable sequence controller for displaying a sequence block on a screen of a cathode-ray tube display unit in the form of ladder diagram. The sequence block display system is provided with a data processor and a buffer memory which includes first, second and third memories. The first memory is capable of storing the whole of sequence programs stored in the sequence controller and the second memory is capable of storing at least one sequence block. The third memory is adapted to store output instructions, which are used to designate a sequence block, in the same order as each designated sequence block is displayed on the screen and further to read out the output instructions in the reverse order for displaying the sequence blocks which are put out of the screen.