Siemens SIMATIC S5-100U System Manual page 86

Start-up and Program Tests
During the program check, you can execute the following additional test and programmable
controller functions from the programmer:
• Input and output (program modification possible)
• Direct signal status display (STATUS VAR)
• Forcing of outputs and variables (FORCE, FORCE VAR)
• Information functions (ISTACK, BSTACK)
If the function is aborted due to hardware faults or program errors, the programmable controller goes
into the STOP mode and the red LED on the control panel of the CPU lights.
Refer to your programmer manual for information about calling up these functions on your
programmer.
4-12
S5-100U
EWA 4NEB 812 6120-02b