IAI America REXT - Manual (Page 208)


Part 1 Specification
Chapter 3 Gateway R unit
184
Part 1 Specification
3.9.4.2 What Is Function Block?
(1) Overview
A function block is a graphical program language for PLCs. It is one of the five program languages for PLCs defined by
the IEC standard (IEC 61131-3).
Ladder logic (or ladder language) currently adopted by the largest number of PLCs is also one of the above five program
languages.
A function block is a program element that allows a group (block) of typical processes (functions) to be created
beforehand, so that they can be used simply by placing the function block in a program and setting the inputs and
outputs.
Basically all typical processes are defined by “variables” instead of actual addresses. When the block is placed and used
in a program, a parameter (address or value) is set for each of these “variables.”
As explained above, a function block is a function having one or more input parameters and one output parameter. It
performs calculation based on the values given to each input parameter and outputs the result to the output parameter.
Use of function blocks allows for modular program design and reuse of programs, thereby reducing the hassle of creating
PLC programs.
Function Block A
Program
Copy of function block A
(Instance)
Created beforehand
Each function block is saved as a file
o Managed in a library
Typical processes
(defined by variables)
Input
(Setting)
Variable Variable Output
(Setting)
Copy of function block A
(Instance)
Input
(Setting)
Variable Variable Output
(Setting)
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