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3-2

Ladder Logic (LAD) for S7-300 and S7-400

C79000-G7076-C504-02

3.1 Creating Logic Blocks – Overview

Logic blocks (OBs, FBs, FCs) are made up of a variable declaration section

and a code section. They also have certain properties. When programming,

you must edit the following three sections:

S Variable declaration table: In the variable declaration table, you declare

the parameters, the system attributes for parameters, and the local

variables of your block.

S Code section: In the code section, you program the block code that is to

be executed by the programmable controller. This consists of one or more

networks with Ladder elements.

S Block properties: The block properties include additional information,

such as a time stamp and a path name, which is entered by the system

itself. In addition to these items you can enter further details about the

name, family, release and author and can assign system attributes for

blocks (see Chapter 5).

The order in which you edit the three sections is irrelevant and you can, of

course, make corrections and additions.

When you refer to symbols from the symbol table, you should make sure that

they are complete and, when necessary, add any missing information.

Save the block

Edit the variable declaration table

for the block

LAD Editor

Make the settings for the editor

Create a logic block (FB, FC or OB)

in the SIMATIC Manager.

Enter the block properties

Edit the code section

Figure 3-1 Procedure for Creating Logic Blocks in LAD

Logic Blocks

Editing a Logic

Block

Creating Logic Blocks

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