Copyright Goodheart-Willcox Co., Inc. Chapter 6 PLC Programming 117 Figure 6-42 shows the interlocking contacts arrangement of an output and a bit. Pressing the green push- button (GPB) at address I:1/0 turns on the G-PLT output light at address O:2/0. Pressing the same button again turns off the light. The B3:0/0 bit retains the previous state of the G-PLT output at address O:2/0. Therefore, the B3:0/0 bit allows the use of a single input (GPB at I:1/0) to toggle the output O:2/0 back and forth between the on and off states. Press the Green Pushbutton (GPB) to turn the Green Pilot Light (G-PLT) on. Press the GPB again to turn the G-PLT off. 000 001 002 B3:0/0 Previous State End I:1/0 GPB I:1/0 GPB I:1/0 GPB I:1/0 GPB O:2/0 G-PLT O:2/0 G-PLT B3:0/0 Previous State B:0/0 Previous State O:2/0 G-PLT Goodheart-Willcox Publisher Figure 6-42. PLC ladder logic diagram for Example 6-5, showing how to use one input to toggle an output between on and off. Example 6-5