Programmable: PLCs are programmable devices, because you can write custom software (as ladder logic, function blocks, or structured text) to define the behavior of the controller. So this programming allows you to specify how the PLC respond to different input conditions and control various output devices.

Logic: The term “logic” refers to the decision-making capabilities of the PLC. Because it is based on the programmed logic, and PLC can execute actions or sequences of actions in response to input signals. So this logic can range from simple on/off control to complex that involve timing, sequencing, and mathematical calculations.