Siemens SIMATIC S5 User Manual

S5-115F Manual Introduction to STEP 5
Figure 2-4 shows how to set up a structured control program. It also illustrates the significance of
organization blocks.
Figure 2-4. Example of Organization Block Use
FB 200FB 2
OB 1
OB 21
System Program
PB 1 SB 1
Control Program
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The functions of the various organization blocks are described on the following pages.
OB 1: Cyclical program scanning
Control program structure is established in OB 1. Using a number of block calls in OB 1, you can
specify the PB or FB processing sequence. Calls can be conditional or unconditional.
OB 2: CPU 942F interrupt handling
CPU 942F implements ”interrupt-driven” processing. Interrupt-driven processing occurs when a
signal from the process causes the CPU in the PLC to interrupt cyclic scanning and to execute a
specific program. After the CPU has executed the special program, it returns to the point of inter-
ruption in the cyclical program and continues scanning from there. The interrupt is triggered by
digital input modules with process interrupt capability.
EWA 4NEB 811 6149-02 2-9

Siemens SIMATIC S5 Specifications

General

Product type designation	SIMATIC S5
Programming language	STEP 5
Digital inputs	Varies by model
Digital outputs	Varies by model
Analog inputs	Varies by model
Analog outputs	Varies by model
Supply voltage	24V DC
CPU Type	Varies by model
Memory	Varies by model
Digital I/O	Varies by model
Analog I/O	Varies by model
Communication	PROFIBUS
Operating Temperature	0°C to 60°C
Relative Humidity	5% to 95% (non-condensing)