Building a Ladder Logic Program

There are several Help Topics which cover individual actions within editing a ladder rung.

This Topic covers basic InstructionInsertion and Configuration, Ladder Scan Execution and suggestions for good programming fundamentals.

Accessing Building a Ladder Logic Program

Building a Ladder Logic Program is accessed from the Help Menu located on the Main Menu.

Instruction Insertion

There are four methods for inserting instructions into the ladder rung.

Method 1:

From the Instruction List located to the right of the Main Screen, Click, Drag and Drop the Instruction to the desired location in the Ladder Editor Window.

Method 2:

Select the location on the rung for the instruction. Then Double Click the desired Instruction in the Instruction List and it will populate the current cursor location, indicated by the blue square.

Method 1 or 2 will give you the results shown below.
Method 3:

Select the location on the rung for the instruction. Then begin typing the Instruction abbreviation, i.e. NO for Normally Open. The following auto-complete box will open.

Continue typing to narrow down your selections or select the down arrow to drop down a list of Instructions. Click on the desired Instruction and select OK to insert into the ladder rung.

Method 4:

Entering an existing or new Tag Name in ladder instead of an instruction abbreviation will pop up the Instruction Shortcut window. You have the freedom to choose from a list of instructions in the drop down, either contacts or coils, to quickly add a new tag without having to enter the instruction first. This is a quicker method of entering tags into ladder.

Instruction Configuration

Once the Instruction has been selected, the configuration window appears. Fill in the necessary data fields with Constant Values or Tags as required.

To select a Tag from the Tag Database, click on the browse icon . This opens the Tag Picker, which gives you a quick and easy way of viewing and selecting a tag.

Ladder Scan Execution

As a principal rule, ladder execution is always “Top to Bottom then Left to Right”. As shown by the diagram below, the ladder execution begins at the top of the program (Rung #1) and scans all conditional contacts from left to right, updates the output, then proceeds to the next rung.

For more details on ladder logic scan execution, see the Logic Scan Behavior topic.

Programming Fundamentals

Each and every programmer has their own programming methods. However, there are a few fundamental recommendations you can follow that may save you time.

Review your electrical schematics and make a list of all physical Inputs & Outputs.
For a Tag-based controller, you may find it more productive to create your Tag Database prior to beginning your ladder logic program.
Group registers with practical naming conventions. i.e. Reject Cylinder Extend Limit Switch or PreHeat Oven Zone1 Temp.
Create an Outline or Flow Chart for your process. Putting your machine control or process on paper in a structured form will help you design your control logic.
Place setup or initialization code at the very beginning of your program or place it in the “Run First Scan Only” Task.
Group sections of ladder code into separate tasks to organize your project, improve performance and simplify troubleshooting.
Learn your instruction set. There are many tasks that can be accomplished manually in ladder logic that may be made easier by specific Function Blocks designed for that task.

Note: The maximum number of rungs allowed per task is 4096.