PLC Programming

4 - The Individual Components
The command for forcing a variable, which means that it will be entered into the forcelist can be found
at the following places:
• Command 'Force Values' in the menu 'Online'.
• Button 'Force Values' in the dialog 'Editing the writelist and the forcelist'.
Note:
In the sequential function chart language, the individual values from which a transition expression is
assembled cannot be changed with 'Force values'. This is due to the fact that in monitoring the 'Total
value' of the expression, not the values of the individual variables are displayed (e.g. "a AND b" is
only displayed as TRUE if both variables actually have the value TRUE).
In FBD, on the other hand, only the first variable in an expression, used for example as input to a
function block, is monitored. Thus a 'Force values' command is only possible for this variable.
'Online' 'Release force'
Shortcut: +
This command ends the forcing of variable values in the controller. The variable values change again
in the normal way.
Forced variables can be recognized in Monitoring by the red color in which their values are displayed.
You can delete the whole forcelist, but you can also mark single variables for which the forcing should
be released.
To delete the whole forcelist, which means to release force for all variables, choose one of the
following ways:
• Command 'Release Force' in menu 'Online'.
• Button 'Release Force' in dialog 'Editing the writelist and the forcelist'
• Delete the whole forcelist using the command 'Release Force' in the dialog 'Remove Write-
/Forcelist'. This dialog opens if you choose the command 'Release Force' while also a writelist
exists.
To release force only for single variables you have to mark these variable first. Do this in one ways
described in the following. After that the chosen variables are marked with an turquoise extension
:
• A double mouse click on a line, in which a non boolean variable is declared, opens the dialog
'Write variable '. Press button .
• Repeat double mouse clicks on a line in which a boolean variable is declared to toggle to the
display at the end of the line.
• In the menu 'Online' open the Write/Force-Dialog and delete the value in the edit field of the
column 'Forced value'.
When for all desired variables the setting "" is shown in the declaration window,
choose the command 'Force values' to transfer the modifications of the forcelist to the program.
If the current writelist (see 'Online' 'Write Values') is not empty while you execute the command
'Release Force', the dialog 'Remove Write-/Forcelist' will be opened. There the user has to decide
whether he just wants to Release Force or additionally wants to Remove the writelist or if he wants
to remove both lists.
CoDeSys V2.3 4-57