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Entry type: FAQ Entry ID: 23967880, Entry date: 06/13/2008
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How are block parameters labeled specially for read-back?

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You can backup or read back the parameters of all the CFC charts contained in the current chart and whose AS data has been changed through OS operations, for example. This applies, for example, to limit values and control parameters.
Instructions
To open the dialog for reading back block parameters you select the menu item "Chart > Read Back..." in the CFC editor.
In PCS 7 V6.1 another selection option for defining the scope for the read-back of parameters has been added. With this version and higher you can also read back in particular "Designated parameters" in addition to the "All parameters" and "OCM-capable parameters" options.
  

Fig. 01

Options in the dialog box "Read Back":

  • All parameters: All parameters capable of being read back that do not have the identifier "S7_read_back = 'false'" are read back.
  • OCM-capable parameters: Only parameters capable of being read back that have the identifier "S7_m_c = 'true'" and that do not have the identifier "S7_read_back = 'false'" are read back.
  • Designated parameters: Only parameters capable of being read back with the identifier "S7_read_back = 'true'" are read back.

Irrespective of the settings the following parameters are generally not read back:

  • Output parameter "OUT"
  • Inputs for which the SFC has write access
  • Subsequently changed blocks. (Different off and online versions)
  • Data types: ANY, ARRAY, POINTER, UDTYPE

Notes
The attribute "S7_read_back" is not usually defined for the block parameters of the PCS 7 standard libraries, this means you must label the relevant block parameters yourself for read-back. For user-created blocks you should set the system attribute "S7_read_back" to "TRUE" for all the relevant parameters when creating the block (in the STL or SCL source, for example).

 


Fig. 02

For blocks that you have not created yourself (blocks from PCS 7 standard libraries, for example) you normally do not have the associated source available. In this case you proceed as follows to label parameters for read-back.
 

No. Procedure
1 Open block for editing
In the Component view you double-click on a block whose parameters are to be labeled for read-back. The block is opened for editing.
   

Note
When you open protected blocks an additional window usually opens with the message: "The block is protected". Click "OK" to acknowledge the window. Only the IO interface parameters are shown for protected blocks.

2 Assign system attribute S7_read_back for block parameters
Under "Interface" you select a parameter that is relevant for read-back. Right-click to open the pop-up menu and select the "Object Properties..." item. The "Properties - Variable" dialog opens. Switch to the "Attributes" tab. In an empty line you insert the attribute "S7_read_back=true".
   

Note
When you select an input field for assigning the system attributes, there is a button on the right side which you can use to open a selection window for all possible inputs. Make your entries in this selection window and thus avoid typographical errors.

 


Fig. 03
 

Click the "OK" button to close the dialog.

 


Fig. 04
 

Repeat this step for all block parameters that are to be read back with the "Designated parameters" option.

3 Save block
Save the block with the menu item "File > Save".

4 Close block
Close the block with the menu item "File > Close".

5 Import block type into chart folder
Since the block's interface has been changed you have to reimport the block type. For this you select "Tools > Block types..." in the CFC editor. The "Block types" dialog opens. In the left selection window "Offline block folder" you select the relevant block. Use the arrow key to transfer the block into the "Chart folder" list on the right. Acknowledge the "Do you really want to use the new version of the block types?" message window with "Yes".

Now you can read back the block parameters.

Additional Keywords
GMP, Pharma, Life Science, Validation, FDA 21 CFR Part 11

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