Siemens SIMATIC S5 Manual page 76

Introduction to STEP 5
• Control system flowchart (CSF)
CSF represents logic operations with symbols.
• Ladder diagram (LAD)
LAD represents control functions with circuit diagram symbols.
Each method of representation has its special characteristics. Consequently, a program block that
has been programmed in STL cannot necessarily be output in CSF or LAD form. The graphic
representations are not compatible to each other either. However, programs in CSF or LAD can
always be converted to STL. Figure 2-1 illustrates these points in a diagram.
Figure 2-1. Compatibility of STEP 5 Methods of Representation
Note
During the individual system acceptance test of the safety-related S5-115F, the
inspector also checks your program. For this reason, the user program must be simply
structured and easy to read.
Write your programs mainly in the CSF form of representation.
Operations which cannot be represented as CSF or LAD must be written in STL net-
works.
Divide your OBs, PBs and SBs into:
• CSF or LAD networks
and
• STL networks
The STEP 5 programming language has the following three operation types:
• Basic operations
• Supplementary operations
• System operations
2-2
CSF
STL
LAD
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S5-115F Manual