Data Block (Db) - Siemens S7-1200 System Manual

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Programming concepts

6.3 Using blocks to structure your program

Using a single FB with DBs

The following figure shows an OB that calls one FB three times, using a different data block

for each call. This structure allows one generic FB to control several similar devices, such as

motors, by assigning a different instance data block for each call for the different devices.

Each instance DB stores the data (such as speed, ramp-up time, and total operating time)

for an individual device.

In this example, FB 22 controls three separate devices, with DB 201 storing the operational

data for the first device, DB 202 storing the operational data for the second device, and DB

203 storing the operational data for the third device.

Data block (DB)

You create data blocks (DB) in your user program to store data for the code blocks. All of the

program blocks in the user program can access the data in a global DB, but an instance DB

stores data for a specific function block (FB).

The data stored in a DB is not deleted when the execution of the associated code block

comes to an end. There are two types of DBs:

● A global DB stores data for the code blocks in your program. Any OB, FB, or FC can

access the data in a global DB.

● An instance DB stores the data for a specific FB. The structure of the data in an instance

DB reflects the parameters (Input, Output, and InOut) and the static data for the FB. (The

Temp memory for the FB is not stored in the instance DB.)

Although the instance DB reflects the data for a specific FB, any code block can access

the data in an instance DB.

You can also modify and download data blocks in RUN mode (Page 808).

S7-1200 Programmable controller

System Manual, 03/2014, A5E02486680-AG