CONTROLLER

PURPOSE:To recognize action timing between devices by inputting action information transmitted/received through a communication channel, time-serially storing and holding it and, simultaneously, providing an information input/output device to output the stored and held action information at any time. CONSTITUTION:Each internal information is time-serially stored in ring memories 22, 32, 42 and 52 at a definite sampling interval at each device, and simultaneously, even an instruction/completion signal transmitted/received with a PC 10 is stored, as well. Further, from respective interfaces 21, 31, 41 and 51, the internal information of respective devices is successively outputted to an inter- device data line 90 for at every interval of the prescribed time. The stored internal information is outputted through maintenance tool interfaces 23, 33, 43 and 53 to a maintain tool 80 as necessary. By using the maintenance tool 80, a fault diagnosis, the detection of the action timing, etc., are executed.