Siemens Memory Specifications download pdf (Page 32)

3 General Programming

3.2 Program blocks

Programming Guideline for S7-1200/1500

V1.2, Entry ID: 81318674

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3.2.3 Function blocks (FB)

Figure 3-6: “Add new block” dialog (FB)

FBs are blocks with cyclic data storage, in which values are permanently stored.

The cyclic data storage is realized in an instance DB.

Figure 3-7: Calling a function block

Call of a function block in the

block editor

Instance DB

Properties

 FBs are blocks with cyclic data storage.

 Temporary and out tags are undefined when called in non-optimized blocks. In

optimized blocks, the values are always preset to the default value (S7-1500

and S7-1200 Firmware V4). Thus, the resulting behavior is not accidental but

reproducible.

 Static tags keep the value from cycle to cycle

Recommendation

 Use the function blocks in order to create subprograms and structure the user

program. A function block can also be called several times in different locations

of the user program. This makes programming of frequently recurring program

parts easier.

 If function blocks are applied multiply in the user program, use separate

instances, preferably multi-instances.

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Siemens Memory Specifications Page 32