Timer Blocks; Multi-Instances - Siemens SIMATIC S7-1200 Safety Programming Manualline

4 Optimizing Safety Programs
4.1.2

Timer blocks

Timers are an integral part of a safety program as many of the system functions
such as "ESTOP1" internally use these timers. Despite this fact, generating a fail-
safe time value requires considerable effort and regeneration for each single timer
block.
Recommendation
Reduce the number of timer blocks to a minimum.
4.1.3

Multi-instances

Recommendation
Use multi-instances for fail-safe function blocks. This means that the block-internal
tags are integrated into the block interface of the calling block.
Advantages

Standardization of safety programs:
No global data is used for block tags. This allows reuse of the calling block
(including the integrated blocks).

Optimizing the compile performance:
–
Using multi-instances requires less protection code than using instance
data blocks.
–
The use of multi-instances reduces the number of F-blocks on the system
side. This optimizes the compilation of the safety program.
Safety Programming Guideline
Entry ID: 109750255, V1.0, 10/2017
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