From the course: PLC Program Flow and Control Instructions

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Introduction to subroutines

Introduction to subroutines - Ladder Logic Tutorial

From the course: PLC Program Flow and Control Instructions

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Introduction to subroutines

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- When you have a Long Ladder Logic Program, depending on the application, oftentimes, it's better to kind of chop the program into smaller pieces when applicable. The smaller pieces are called subroutines. A subroutine is a short program that is used by the main program to perform a specific function. The subroutines are called and executed from the main program, as you can see in the illustration here. Each subroutine must have a unique file number. This is how it works. When a subroutine is called from the main ladder logic program, the program is able to scape and go to a subroutine to perform certain functions and then, return to the main program. The main program is called the Main Routine. Sometimes a portion of the Ladder Logic Program must be repeated several times, during, for example, one machine cycle. The subroutine can save a great deal of duplicate programming. The sequence of rungs could be…

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