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Entry type: FAQ Entry ID: 17376617, Entry date: 09/17/2007

What is the difference between offline and online processing in the LAD/STL/FBD editor?

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Configuration Notes:
During the test phase or commissioning it is often necessary to make minor changes to the blocks. If the associated user program is on a programming device, there are always two different procedures for making changes.

No. Difference between offline and online editing of blocks
1 Online change
The block is opened and edited from the block folder in the Online window of the SIMATIC Manager. The changes are saved offline on the programming device in the LAD/STL/FBD editor via
  • "File > Save" or via the floppy disk icon in the toolbar.

Then the program is loaded into the CPU either via

  • "PLC > Load" or via the load icon in the toolbar.
2 Offline change
The block is opened, changed and saved in the Offline block folder. After loading in the LAD/STL/FBD editor via
  • "PLC > Load" or via the load icon in the toolbar

the block can then be loaded into the CPU and monitored.

In principle it is preferable to use the Offline change function, because most work steps are made offline. This gives you a slight time advantage in editing. If the user program is not in the programming device, you can load and edit the blocks from the CPU into the programming device via

  • "PLC > Load into PG" or via
  • "PLC > Load station into PG..."

. In this case, however, the icon information and comments are no longer available. This version is therefore mainly applicable for service cases.

More information on this is available in the Online Help of STEP 7 under "Uploading from the Programmable Controller to the PG/PC".

If you have made changes to your program in the LAD/STL/FBD editor, the function "Test > Monitor" and the button with the spectacles cannot be activated and are grayed out. After saving you can reactivate the "Monitor" function. When you activate the "Monitor" function, a message is displayed indicating that the edited block shown cannot be monitored, because it doesn't match the block on the CPU. Click on the "Yes" button and the block shown is loaded onto the CPU and you can monitor it.

Fig. 01

If, however, you only want to monitor the block on the CPU (without the changes in the Offline project), then click on the "No" button and select the menu "File > Open online". The block in the CPU is shown and you can restart the function.

In some cases you have to delete the old block in the CPU first before you load the changed block into the CPU. It might happen that the CPU's memory is practically full. To enable online downloading without program interruption, you must store the new block version with overwriting a second time in the main memory. The old block is deleted only when the new version of the block is written completely in the CPU. If the main memory limit is exceeded in doing this, a download can only be made after you have manually deleted the old block in the Online container. This means that a block cannot be overwritten in the CPU if the memory required by the new version is greater than the remaining free memory in the CPU.

Updating a data block in the offline project:
You use a global DB and would like to upload the changes, which you have made in the online DB, back into the offline project. If the variables match, only the content of the offline DB is overwritten. Click "Yes" to acknowledge the dialog box (Fig. 02).

Fig. 02

However, if the structure of the DB has been changed in the CPU (e.g. if other variables have been inserted into the online DB), you should rename the offline DB and only upload the online DB afterwards. You can then open the two DBs and recopy any newly created variables from the online DB into the offline DB.

30:484, Program development, Text function

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