Structured Programming - Siemens SIMATIC S5-90U System Manual

Introduction to STEP 5
7.2.2

Structured Programming

To solve complex tasks, it is advisable to divide a program into individual, self-contained program
parts (blocks).
This procedure has the following advantages:
• Simple and clear programming, even for large programs
• Capability to standardize program parts
• Easy alteration
• Simple program test
• Simple start-up
• Subroutine techniques (block call from different locations)
• Lower scan time extension through "STATUS" PLC function.
The STEP 5 programming language has the following five block types.
• Organization Blocks (OBs)
Organization blocks manage the control program.
• Program Blocks (PBs)
Program blocks arrange the control program according to functional or technical aspects.
• Sequence Blocks (SBs)
Sequence blocks are special blocks that program sequence controls. They are handled like
program blocks. (They can be used only in the S5-95U).
• Function Blocks (FBs)
Function blocks are special blocks for programming frequently recurring or especially complex
program parts (e.g., reporting and arithmetic functions). You can assign parameters to them (in
the S5-95U). They have an extended set of operations (e.g., jump operations within a block).
• Data Blocks (DBs)
Data blocks store data needed to process a control program. Actual values, limiting values, and
texts are examples of data.
7-4
S5-90U/S5-95U
EWA 4NEB 812 6115-02b