Technical data

Table Of Contents
System Software for S7-300/400 System and Standard Functions - Volume 1/2
A5E00709327-01
1-1
1 Organization Blocks
1.1 Overview of the Organization Blocks (OBs)
What Are Organization Blocks?
Organization Blocks (OBs) are the interface between the operating system of the
CPU and the user program. OBs are used to execute specific program sections:
At the startup of the CPU
In a cyclic or clocked execution
Whenever errors occur
Whenever hardware interrupts occur.
Organization blocks are executed according to the priority they are allocated.
Which OBs Are Available?
Not all CPUs can process all of the OBs available in STEP 7. Refer to Operations
lists /72/ and /102/ to determine which OBs are included with your CPU.