Sequentially number the output modules

In the following I/O diagram, the first output card encountered is the OA16. Although it is not in the first slot, its address will be "O:0" ("OHH, colon, ZERO"). This module consumes one datatable word. Therefore, the addressing of the next OUTPUT module, moving from left to right, will begin with "O:1," regardless of the module's physical location.

I/O Diagram