Siemens SIMATIC S7-1200

Online and diagnostic tools
15.13 Monitoring and modifying values in the CPU
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
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15.13.4
Using a watch table to monitor and modify values in the CPU
A watch table allows you to perform monitoring and control functions on data points as the
CPU executes your program. These data points can be process image (I or Q), M, DB or
physical inputs (I_:P), depending on the monitor or control function. You cannot accurately
monitor the physical outputs (Q_:P) because the monitor function can only display the last
value written from Q memory and does not read the actual value from the physical outputs.
The monitoring function does not change the program sequence. It presents you with
information about the program sequence and the data of the program in the CPU.
Control functions enable the user to control the sequence and the data of the program. You
must exercise caution when using control functions. These functions can seriously influence
the execution of the user/system program. The three control functions are Modify, Force and
Enable Outputs in STOP.
With the watch table, you can perform the following online functions:
● Monitoring the status of the tags
● Modifying values for the individual tags
You select when to monitor or modify the tag:
● Beginning of scan cycle: Reads or writes the value at the beginning of the scan cycle
● End of scan cycle: Reads or writes the value at the end of the scan cycle
● Switch to stop
To create a watch table:
1.
Double-click "Add new watch table" to open a new
watch table.
2.
Enter the tag name to add a tag to the watch table.
The
following options are available for monitoring tags:
•
Monitor all: This command starts the monitoring of
the visible tags in the active watch table.
•
Monitor now: This command starts the monitoring
of the visible tags in the active watch table. The
watch table monitors the tags immediately and
once only.
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.