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4-2

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

C79000-G7076-C504-02

4.1 Creating Data Blocks – Overview

Data blocks (DBs) are used to handle data which is why they do not have a

code section. Programming data blocks involves the following :

S Declaration table: The declaration table is where you specify the data

structure of the data block.

S Block properties: These include extra information such as time stamp,

programming language and path name, which is all entered by the system

itself. You can also add information about the name, family, version and

author and you can assign system attributes for blocks (see Chapter 5).

A user program can have the following data blocks:

S Shared DBs can be accessed by all logic blocks in the program. The data

remains stored in the data block even when it has been closed.

If you require several shared DBs of the same data structure, you can

create them with the help of a UDT. These are data blocks with an

associated user-defined data type.

S Instance DBs are associated with specific function blocks and are

structured according to the declaration table of the FB. You can only

create an instance DB if the corresponding function block exists. They are

data blocks with an associated function block.

Depending on the type of data block you want to create, different methods

are used.

Shared data blocks can be created as follows:

S Define the structure for a single data block. For this you must define the

variables and data types in the desired order. This structure only applies to

this DB.

S Define the structure for the data block with the help of a user-defined data

type. In this case the UDT structure defines the data structure of the DB.

A user data type can be assigned to a number of data blocks.

Create an instance data block and then:

S Assign an existing function block to the data block. In this case the

declaration section of the function block defines the structure of the data

block. A number of instance data blocks can be assigned to one function

block.

Data Blocks

Types of Data

Blocks

Methods of

Creating Data

Blocks

Creating Data Blocks and User-Defined Data Types

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