505-4332 | Siemens 24 VDC Input Module

To relate the hardwired connections on the equipment that you arecontrolling to the program inputs and outputs, you need to focus on thefunction of the image register. For normal I/O updates, the interfacebetween the software RLL program and the physical hardware occurswithin the image register. Refer to Figure 3-4 for an example of the discreteoperation in which a limit switch controls the state of a pilot light.During the next I/O update, the controller reads the state of the input point from the module, and writes a 1 to X69 in the discrete image register. Note that Y16 is off, and so the controller writes a 0 from Y16 to the output module during this I/O update (not shown in the diagram).