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S5-100U
7.3.1
Organization Blocks
Organization blocks (OB) form the interface between the operating system and the control program.
Organization blocks are handled in one of the following three ways:
•
Organization block OB1 is called cyclically by the operating system.
•
Some organization blocks are event-driven or time-controlled. They can be called in response
to events or at certain times:
-
By a switch from STOP to RUN (OB21)
-
By a switch from Power OFF to Power ON (OB22 (see Table 7-3))
-
By interrupts (OB2 and OB13)
•
Some other organization blocks represent operating functions (similar to the the integral function
blocks). They can be called by the control program (for CPU 103 and higher; see section 9.3).
Table 7-3 provides an overview of organization blocks.
OB No.
You must program the OB. The operating system calls up the OB.
OB1
Cyclic program processing
Interrupt-driven program processing
OB2
Interrupt-driven program processing
OB13
Time-controlled program processing
Handling start-up procedures
OB21
When starting manually (STOP to RUN)
OB22
When power returns
Handling programming errors and device errors
OB34
Battery failure
The OB is already programmed. You must call up the OB.
OB31
Scan time triggering (resets scan time monitor)
OB251
PID control algorithm
OB is ready or is supported by the operating system
You can program all organization blocks using parameters from the permissible range. CPU 100
and CPU 102 use organization blocks OB0 to OB63. CPU 103 uses OB0 to OB255. However, you
must call the organization blocks from the control program.
EWA 4NEB 812 6120-02
Table 7-3. Overview of Organization Blocks
Function
Introduction to STEP 5
OB integrated in
CPU 100
CPU 102
CPU 103
7-9
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