Minecraft wiki entry for Redstone_circuits, associated text: A "diode" is a one-way circuit that allows a signal to travel in one direction. It is used to protect another circuit from the chance of a signal trying to enter through the output, which could incorrectly change the circuit's state or interfere with its timing. It is also used in a compact circuit to keep one part of the circuit from interfering with another. Common choices for a diode include a redstone repeater or a height elevation to glowstone or an upside-down slab, which does not transmit a signal back down.