CHECKING DEVICE FOR EXTENSION BUS OF PROGRAMMABLE CONTROLLER

摘要

PURPOSE:To surely detect the abnormality by transferring the check data to the extension unit of the final stage via all extension bus signal lines to adversely transfer the check data again via said signal lines and comparing the transferred data and the adversely transferred data. CONSTITUTION:A selector 32 and a reception side control circuit 42 of an extension unit 9 of the final stage are set in a check processing state respectively by a check mode signal 37 of a control signal generating circuit 36 of a basic unit 1. The extension bus check data is written into a storage device 39 and at the same time sent onto an extension bus address signal line 34. The circuit 42 stores the bus check data into a reception data storage device 40. Then the data stored in the storage device 40 is sent again onto the line 34 and stored in a reread signal storage device 48. This data is compared with the check data stored in the storage device 39 by a comparator 49. If no coincidence is obtained from said comparison, a noncoincidence output signal 50 is activated. In such a way, the short circuit or the release of an extension bus signal line can be surely detected.