Siemens SIMATIC S7 System Manual page 570

Debugging and troubleshooting
10.2 Displaying program status
Example program status in the LAD program editor
The example below shows status in the LAD program editor. The program editor displays the
values of operands and indicates powerflow as each instruction executes during the execute
program phase of a scan cycle.
Example program status in the FBD program editor
The example below shows status in the FBD program editor. The red color of the ADD_I
instruction box indicates errors in the operands.
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System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART