Siemens SIMATIC S5-90U System Manual page 108

Diagnostics and Trouble Shooting
5.3 Interrupt Analysis Using the Programmer
The operating system sets various "analysis" bits in the case of any malfunction. These bits can be
read by means of the ISTACK function of the programmer.
5.3.1 "ISTACK" Analysis Function
The interrupt stack is an internal programmable controller memory area where the causes of mal-
functions are stored. If there is a malfunction, a bit in the respective byte of the memory area is
set.
You can read out the contents of this memory area using the programmer.
ISTACK Call
The call is made through the programmer menu in the "STOP" operating mode.
Refer to your programmer manual for the key sequence.
NOTE
In the RUN mode, only the control bits can be output in the ISTACK function.
Updating the ISTACK
The ISTACK is updated automatically in the following cases:
• When the PLC changes from "RUN" to "STOP"
• If the PLC remains in the "STOP" mode although you have switched the operating mode switch
from "STOP" to "RUN".
If you now call up the ISTACK on the programmer, the current cause of the malfunction will be
displayed.
The tables on the following pages inform you of the following:
• Which control bits are output in the ISTACK
• Which causes of malfunctions are output in the ISTACK;
• Descriptions of the abbreviations and error IDs used in the ISTACK display.
5-4
S5-90U/S5-95U
EWA 4NEB 812 6115-02b