Safety Programming Guideline
Entry ID: 109750255, V1.0, 10/2017
Depending on the application, it is not always possible to use all the suggestions.
However, they show why certain programming methods cause shorter
compilation and program runtimes than a non-optimized program.
Determining the runtime
TIA Portal automatically creates a data block, "RTGxSysInfo", for each F-runtime
group. Among other things, this block contains the current and the longest runtime
of this F-runtime group.
You will find this system-generated block in the project tree ("Program blocks >
System blocks > STEP 7 Safety").
Figure 4-2: System-generated DB: "RTGxSysInfo"
4.1.1 Jumps in the safety program
In a standard user program, a jump from one network to another (jump to label) or
from the block (return) is a simple program branch that is recalculated for each
cycle but not additionally protected. This means there is no check whether or not,
for example due to a memory error caused by EMC, a jump takes place despite the
"false" condition.
This is not allowed in a fail-safe program as it must be ensured at all times that the
program is in the correct branch.
This requires that both alternatives (jump to label is "true" or "false") be calculated
in their entirety in the protection program.
The more jumps you use in a safety program, the greater the influence on the
controller's performance.
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