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4 Optimizing Safety Programs

Note

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.

Safety Programming Guideline

Entry ID: 109750255,

V1.0,

10/2017