Basic Instructions and Scan Cycle
In this lesson we are going to go step by step in depth of how we ended up with the results of your last rung wins scenario.
This is where many of the "rules", such as only using an output coil twice, come from. While we completely agree that you shouldn't use a double coil such as we did in this lesson series, it is important that you understand how the PLC executes these two rungs. Often we've heard people say "Don't use a double coil because the PLC's were not designed to handle them and it confuses the PLC". PLC's don't get confused, they execute code in a repetitive methodical manner.
You may also be asking yourself, "why would anyone put these two rungs into the same PLC program?". These are two very common rungs for controlling outputs. You might simply type the wrong address into one of the OTEs or there could be hundreds of rungs in between them and you forgot that you added the OTE early on in the program and insert a second rung to control it.