Software 4.2.1 Definitions Inputs Signals that are fed into the controller and read by the user program. Outputs Signals that are generated by the program in the controller and picked up externally as control signals. They switch on lamps, drives etc. Markers Signals that are used inside the controller for storing states and supporting complex logical operations. There are two types of markers: Ш bit markers (1-bit signals) and Ш byte marker (8-bit signals). Timers They control time processes. Counters They count events or increments output by pulse generators. 44