Siemens SIMATIC S7-300 Hardware And Installation Manual page 133

Monitoring variables
You have two options of monitoring variables:
• updating the status values once via menu item Variable > Update status
values
or
• continuous update of status values via menu item Variable > Monitor
Controlling variables
To control variables, proceed as follows:
1. Left-click the field Control value of the respective variable.
2. Enter the control value according to the data type.
3. To update control values once, select the menu item Variable > Enable control
values.
or
Enable control values permanently via menu item Variable > Control.
4. In the Monitor test function, verify the control value entry in the variable.
Is the control value valid?
You can disable the control value entered in the table. An invalid value is displayed
same as a comment. You can re-enable the control value.
Only valid control values can be enabled.
Setting the trigger points
Trigger points:
• The "Trigger point for monitoring" determines the time of update for values of
variables to be monitored.
• The "Trigger point for controlling" determines the time for assigning the control
values to the variables to be controlled.
Trigger condition:
• The "Trigger condition for monitoring" determines whether to update values
once when the trigger point is reached or continuously every time the trigger
point is reached.
• The "Trigger condition for controlling" determines whether to assign control
values once or permanently to the variable to be controlled.
You can customize the trigger points using the tool "Monitor and control variable" in
menu item Variable > Set Trigger ... start.
Special features
• If "Trigger condition for monitoring" is set to once , the menu items Variable >
Update status value or Variable > Monitor have the same effect, namely a
single update.
• If "Trigger condition for controlling" is set to once , the menu items Variable >
Update control value or Variable > Control have the same effect, namely a
one-time assignment.
• If trigger conditions are set to permanent , the said menu items have different
effects as described above.
• If monitoring and controlling is set to the same trigger point, monitoring is
executed first.
S7-300 Programmable Controller Hardware and Installation
A5E00105492-01
Commissioning
8-21