In electronics, the terms "Falling Edge" and "Rising Edge" refer to the transition of a digital signal from high to low (falling edge) or low to high (rising edge), respectively. These transitions are used to trigger events or actions in digital circuits. For example, in microcontrollers, a rising edge of a digital signal may be used to indicate the start of a data transfer or to trigger an interrupt. Similarly, a falling edge may be used to indicate the end of a data transfer or to signal a change in state.

In PLC (Programmable Logic Controller) programming, falling and rising edges are commonly used to detect changes in digital input signals. For example, a rising edge detection can be used to trigger a specific action in the PLC program, such as starting a motor or opening a valve, when a switch or sensor connected to a digital input is activated. A falling edge detection can be used to stop a motor or close a valve when the switch or sensor is deactivated.

In PLC programming, these edges can be programmed using ladder logic, function blocks, or other programming languages, depending on the specific PLC and software being used. By using edge detection, PLCs can respond to fast-changing inputs, ensuring that they respond quickly to changes in the system being controlled.