Industrial control system employing relay ladder objects

Rapid development of control programs for programmable logic controllers controlling semi-standard combinations of equipment is provided by the creation of relay ladder logic objects prestored in the programmable logic controller and invoked only as needed for the particular application. The inability of a programmable logic controller to provide for the memory management mechanisms necessary for true software object instancing is overcome by pre-storing the objects in the programmable controller with pre-allocated variable addresses. Connection of the used objects to I/O is provided by a mapper program also written in relay ladder code. The objects are associated with particular pieces of equipment and provide inter-machine control for that equipment while high level control program executed on a standard computer which controls the objects through reading and writing of object variables.