of the i o module itself is not provided by the software address 83 memory 64 also includes an i o map table 84 shown as a five column multi row table where elements in each row are linked together each software address 83 including all of its extensions associated with a particular i o module starts a separate row of the i o map table 84 thus the i o map table 84 links software addresses 83 identifying a particular i o module 20 to information about the i o module 20 the first piece of information after the software address in each row of the i o map table 84 is the physical address 85 of the i o module 20 providing the interface between the control point 23 and the industrial control system 10 identified by the software address 83 referring to fig3 and 4 the determination of the physical addresses 85 will be described with respect to a more complex control system incorporating a central controller 26 in a rack 12a having three i o modules 20 at slots 3 4 and 5 of an 8 slot rack these slot numbers provide part of the physical address of the i o modules 20 which for clarity will be assumed to equal the slot number although in practice the address of the first slot is normally zero at slot 8 of rack 12a a 34 bridge 34 communication module 24 connects the rack to a communications link 27.