Ladder diagram components

Ladder diagram is one of the languages used to define an operation based on the inputs and outputs from the controller. Create instructions in the routine to break up large or complex ladder diagrams into multiple routines, such as a main routine, a fault routine, and a subroutine. After creating routines, schedule their execution in the program or phase.
Ladder diagram routines contain:
Item
Description
Routines
A sequence of logic that is executed as a block. The main routine is the routine that executes first when the program runs.
Subroutines
Blocks of logic that execute in response to another routine. The main and fault routines jump to the first subroutine when a JSR instruction executes.
Fault routines
Routines that execute when a program fault occurs.
Branches
A parallel logic path within a rung of a ladder program.
Rungs
The composition elements of ladder logic. Ladder logic is comprised of a set of rungs. A rung contains:
  • Rung number. The last rung in a routine is called the End rung and is not editable.
  • Left and right power rails. The area to the left of the power rail is called the rung selection region.
  • Rung wire.
  • Rung state indicator.
Instructions
A mnemonic abbreviation and a data address that define the operation to be performed by the controller. For example, CMP is the mnemonic for performing a comparison between two values.
A program consists of a set of input and output instructions. The controller evaluates Input instructions as True or False. The controller sets the output instructions to True or False in response.
Provide Feedback
Have questions or feedback about this documentation? Please submit your feedback here.