ALWAYS Gate

The ALWAYS Gate is a logic gate that has an output that is initially 0. Once the input variable goes to logic 1 the output also goes to logic 1 and remains in that state. Thus, once the output becomes a logic 1 it will ALWAYS be in the HIGH state and cannot be altered anymore by changes in the input variable. In this circuit the capacitor initializes the output to logic 0 at power-up, assuming that the input will be at logic 0 while the system initializes. The diode provides a discharge path for the capacitor at power-down. The output can be reset by opening the switch and setting the input to logic 0.