Online and diagnostic tools
14.11 Monitoring and modifying values in the CPU
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
799
The following options are available for modifying tags:
● "Modify to 0" sets the value of a selected address to "0".
● "Modify to 1" sets the value of a selected address to "1".
● "Modify now" immediately changes the value for the selected addresses for one scan
cycle.
● "Modify with trigger" changes the values for the selected addresses.
This function does not provide feedback to indicate that the selected addresses were
actually modified. If feedback of the change is required, use the "Modify now" function.
● "Enable peripheral outputs" disables the command output disable and is available only
when the CPU is in STOP mode.
To monitor the tags, you must have an online connection to the CPU.
You use the buttons at the top of the watch table to select the various functions.
Enter the tag name to monitor and select a display format from the dropdown selection. With
an online connection to the CPU, click the "Monitor" button to display the actual value of the
data point in the "Monitor value" field.
Using a trigger when monitoring or modifying PLC tags
Triggering determines at what point in the scan cycle the selected address will be monitored
or modified.
Table 14- 4 Types of triggers
Continuously collects the data
At scan cycle start Permanent: Continuously collects the data at the start of the scan cycle, after
the CPU reads the inputs
Once: Collects the data at the start of the scan cycle, after the CPU reads the
At scan cycle end Permanent: Continuously collects the data at the end of the scan cycle, before
the CPU writes the outputs
Once: Collects the data once at the end of the scan cycle, before the CPU
At transition to
STOP
Permanent: Continuously collects data when the CPU transitions to STOP
Once: Collects the data once after the CPU transitions to STOP
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