PROGRAMMABLE LOGIC CONTROLLER SYSTEM AND MODULE NUMBER ALLOCATING METHOD

PROBLEM TO BE SOLVED: To automatically allocate module numbers by providing a means which allocates individual module numbers to respective input/output(I/O) modules. SOLUTION: A bank (contact terminal group) 42 is formed of adjacently connected I/O modules 24. A module identification system is used not based upon only the relative positions of the I/O modules 24 at a back wiring part. The module numbers are allocated by a numbering protocol based upon left-to- right (rightto-left) succession passing through the respective banks. The numbering through the respective banks 42 is performed in the left-to-right order irrelevantly to whether or not the reception sides of the banks are connected in array to a bus master 12. Namely, the individual module numbers (address) are assigned to the respective I/O modules according to the successive positions of the respective I/O modules for a master controller and the I/O modules of the respective banks which are successively numbers in a specific direction through the respective banks.