Using A Watch Table To Monitor And Modify Values In The Cpu - Siemens S7-1200 System Manual

Online and diagnostic tools
14.11 Monitoring and modifying values in the CPU
6. Save the project to configure the copied values as the new start values for the DB.
7. Compile and download the DB to the CPU. The DB uses the new start values after the
CPU goes to RUN mode.
Note
The values that are shown in the "Monitor value" column are always copied from the
CPU. STEP 7 does not check whether all values come from the same scan cycle of the
CPU.
14.11.4

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
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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.
System Manual, 03/2014, A5E02486680-AG
S7-1200 Programmable controller