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Data Block Access in Step 7 FB/FCs

Function Blocks (FBs) and Function Codes (FCs) in Step 7 access data blocks using a dedicated memory area for static and temporary data. When an FB/FC needs to access data within a data block, it doesn't directly use input/output parameters for all data, especially for persistent data.

How Address Registers are Managed:

• Static Data: Data declared with the STATIC attribute within an FB/FC is stored in the FB/FC's instance data block (DB). This DB is created when the FB/FC is first called. Access to static data utilizes the address registers managed by the Step 7 runtime environment.
• Temporary Data: Data declared without the STATIC attribute is temporary and exists only during the FB/FC's execution. It's stored in the FB/FC's working memory.
• Data Block Access: When referencing data in external data blocks (DBs), the FB/FC uses the DB number and data address (e.g., "DB1.DBX0.0"). The Step 7 compiler resolves these addresses during configuration, and the runtime system manages the memory access.

Key Considerations:

• Avoid excessive use of static data, as it increases memory consumption.
• Optimize data block access for performance.

For detailed information, refer to the following resources within SiePortal:

• Data Blocks
• Function and Function Block Concepts