Siemens Memory Specifications download pdf (Page 51)

3 General Programming

3.6 Symbolic addressing

Programming Guideline for S7-1200/1500

V1.2, Entry ID: 81318674

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3.6.3 STRUCT data type and PLC data types

The STRUCT data type represents a data structure which is made up of elements

of different data types. The declaration of a structure is performed in the respective

block.

Figure 3-27: Structure with elements with different data types

In comparison to structures, PLC data types are defined across the controller in the

TIA Portal and can be centrally changed. All usage locations are automatically

updated.

PLC data types are declared in the “PLC data types” folder in the project navigation

before being used.

Figure 3-28: PLC data types

Advantages

 A change in a PLC data type is automatically updated in all usage locations in

the user program.

Recommendation

 Use the PLC data types to summarize several associated data, such as, e.g.

frames or motor data (setpoint, speed, rotational direction, temperature, etc.)

 Always use PLC data types instead of structures for the multiple uses in the

user program.

 Use the PLC data types for structuring into data blocks.

 Use the PLC data types in order to specify a structure for a data block. The

PLC data type can be used for any number of DBs. You can easily and

conveniently create as many DBs of the same structure and adjust them

centrally on the PLC data type.

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Siemens Memory Specifications Page 51