Function Blocks - Allen-Bradley Micro800 General Instructions Manual

Chapter 1
Finding information about instructions and ladder elements
Item No.
18

Function blocks

A function block is an instruction block that has input and output parameters and
works on internal data (parameters). It can be written in Structured Text, Ladder
Diagram, or Function Block Diagram languages.
Instruction block format
An instruction block is represented by a single rectangle, and has a fixed number of
input connection points and output connection points. An elementary instruction
block performs a single function.
Item Description
Block name The name of the function to be performed by the instruction block is written inside its rectangle shape (at
the top).
Input Each input of an instruction block is labeled and has a defined type.
Input connection Inputs are connected on the left border.
Output Each output of an instruction block is labeled and has a defined type.
Output connection Outputs are connected on the right border.
Calling a function block
When a function block is called in a program, an instance of the block is actually
called. The instance uses the same code, but the input and output parameters are
instantiated, which means local variables are copied for each instance of the
function block. The values of the variables of a function block instance are stored
from one cycle to the other.
A function block can be called by a program, or by another function block. They
cannot be called by functions because functions are not instantiated.
Rockwell Automation Publication 2080-RM001D-EN-E - February 2015