Using A Watch Table For Monitoring The Cpu - Siemens SIMATIC S7-1200 Manual

8.7

Using a watch table for monitoring the CPU

A watch table allows you to monitor or modify data points while the CPU executes your user
program. These data points can be inputs (I), outputs (Q), peripheral inputs or outputs (such
as "On:P", "I 3.4:P" or "Q3.4:P"), M memory, or a DB. 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. You can also use the "Modify" and "Force" functions
to test the execution of your user program.
Note
The digital I/O points used by the high-speed counter (HSC), pulse-width modulation (PWM),
and pulse-train output (PTO) devices are assigned during device configuration. When digital
I/O point addresses are assigned to these devices, the values of the assigned I/O point
addresses cannot be modified by the "Force" function of the watch table.
With a watch table, you can monitor or modify the values of the individual tags. You can also
force a tag to a specific value. You can specify to monitor or modify the tag at the beginning
or the end of the scan cycle, when the CPU changes to STOP mode, or "permanently" (with
the value not being reset after a STOP to RUN transition).
To monitor the tags, you must have an online connection to the CPU. The following options
are available for modifying tags:
● "Modify now" immediately changes the value for the selected addresses for one scan
● "Modify with trigger" changes the values for the selected addresses.
● "Enable peripheral outputs" allows you to turn on the peripheral outputs when the CPU is
The various functions can be selected using the buttons at the top of a watch table. Enter the
tag name to monitor and select a display format from the dropdown selection. With an online
connection to the CPU, clicking the "Monitor" button displays the actual value of the data
point in the "Monitor value" field.
Easy Book
Manual, 11/2009, A5E02486774-01
cycle.
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.
in STOP mode. This feature is useful for testing the wiring of the output modules.
8.7 Using a watch table for monitoring the CPU
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.
Easy to use the online tools
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