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Siemens SIMATIC S7-1200 Programowanie bezpieczeństwa Manualline

4 Optimizing Safety Programs

4.2

Avoiding data corruption

The protection mechanisms within the scope of coded processing (see Chapter 5)

cyclically analyze the program's execution for data corruption. In case of data

corruption, a special system function block triggers an F-STOP of the CPU.

The purpose of this mechanism is to detect influences such as EMC, defect

components, etc. and bring the system to a safe state before the machine

becomes a risk for humans and the environment.

Aside from external influences, data corruption can also be caused by incorrect

programming. The most frequent cause of data corruption is that the standard user

program or an external device (e.g., HMI) writes data while the safety program

reads that data.

This can occur in the following situations:

–

Write access by higher-priority alarms

–

Write access by HMI / communication

–

Use of clock memories

–

Update of a partial PII by higher-priority alarms

For information about how to correctly program access from the standard user

program to the safety program, see Chapter 3.9.

Safety Programming Guideline

Entry ID: 109750255,

V1.0,

10/2017