Hello friends! In the previous ladder-logic introduction , we built AND, OR and NOT conditions using contacts and coils. Today we will combine those building blocks to create NAND, NOR, XOR and XNOR. Each gate answers a different question about its inputs, so understanding the question is more useful than memorizing a diagram. We will retain the original X0, X1 and Y0 examples and walk through their truth tables. Then we will apply the same reasoning to a sensor-disagreement indicator and a command-feedback comparison. These examples make it easier to see why a rung that is logically correct can still be unsuitable for a particular process requirement. Before starting, remember that ladder contacts inspect Boolean data. They do not change the physical input or carry a real voltage through ...