Program Structure And Standard Functions; Organization Blocks (Ob) - Siemens SIMATIC S7-300 Manual For Migrating

5 Software Conversion
5.3

Program structure and standard functions

5.3.1

Organization blocks (OB)

Organization blocks are located in the firmware of the SIMATIC CPU and called by
the CPU's operating system when specific events occur. They are the interface
between the system program and the user program and can be programmed by
the user. S7-300/S7-400 CPUs as well as S7-1500 CPUs have organization
blocks. In some cases, the available OBs differ between the two SIMATIC
platforms.
OBs are processed on a priority-controlled basis (1 stands for lowest, 26 for
highest priority). When there are multiple simultaneous OB requests, the highest
priority OB is processed first. When an event occurs whose priority is higher than
the one of the currently active OB, this OB is interrupted.
The most important OBs are listed below.
Cyclic program processing
Table 5-13
S7-300 CPUs/
S7-400 CPUs
OB 1
Time-controlled program processing (cyclic interrupts)
Table 5-14
S7-300 CPUs/
S7-400 CPUs
OB 32-35/
OB 30-38
SIMATIC S7-1500 provides 20 OBs you can use for time-controlled program
processing. In contrast to S7-300/S7-400, the S7-1500 allows you to individually
set the cycle clock for each cyclic interrupt OB and to individually set the phase
shift. For S7-300/S7-400 it depends on the respective CPU which OBs are
available. For S7-400 CPUs priorities can be set, for S7-300 CPUs this is not
possible.
Program processing during startup (restart)
Startup OBs are processed once when the CPU mode changes from STOP to
RUN. When the startup OB has been processed, cyclic program processing and
cycle time monitoring starts.
In S7-300/S7-400, you could use 3 different startup OBs. Depending on the CPU
startup, the respective OB is then called by the operating system and processed
once. The S7-1500 always runs in warm restart.
Migration S7-300/S7-400 nach S7-1500
Entry ID: 109478811, V1.1,
S7-1500 CPUs
Main OB
S7-1500 CPUs
Cyclic interrupt
OB
05/2017
Description
Cyclic program processing
For S7-1500, multiple cyclic OBs can be used that
are performed in one cycle after the other.
Description
Time-controlled program processing
For program processing at periodic intervals.
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