[PDF] Chapter 2: Basic Ladder Logic Programming Computer Aided Manufacturing TECH 4/53350 8. OR Operation PLC Ladder Logic. Append above to the leading two rungs of relay ladder logic diagram. Switch A and Switch B are connected to discrete input channels of the PLC. Light is connected to discrete output channel (actuator) of the PLC.[PDF] Ladder and Functional Block Programming - Elsevier The input to the top AND gate is: A and B and so its output is: A B Thus the Boolean expression for the output from the OR gate is: A B þ A B ¼ Q Consider a logic diagram with many inputs, as shown in Figure 11, and its representation by a Boolean expression and a ladder rung.