Siemens Simantic ET200SP User Manual

Basics of program execution
7.1 Events and OBs
Distributed I/O system
152 System Manual, 12/2016, A5E03576849-AG
OB priority and runtime behavior
If you have assigned an OB to the event, the OB has the priority of the event. The CPU
supports the priority classes 1 (lowest priority) to 26 (highest priority). The following items are
essential to the processing of an event:
● Calling and processing of the assigned OB
● The update of the process image partition of the assigned OB
The user program processes the OBs exclusively on a priority basis. This means the
program processes the OB with the highest priority first when multiple OB requests occur at
the same time. If an event occurs that has a higher priority than the currently active OB, this
OB is interrupted. The user program processes events of the same priority in order of
occurrence.
Note
Communication
Communication (e.g. test functions with the PG) always works permanently wi
th the priority
15. So as not to unnecessarily prolong program runtime in the case of time
-critical
applications, these OBs should not be interrupted by communication. Assign a priority >15
for these OBs.
Reference
You can find more information on organization blocks in the STEP 7 online help.

Siemens Simantic ET200SP Specifications

General

System Type	Modular I/O System
Mounting	DIN Rail
Power Supply	24 V DC
Category	I/O Systems
Protection Class	IP20
Modularity	Yes
Communication Protocols	PROFINET, PROFIBUS
Digital Inputs	Available (varies by module)
Digital Outputs	Available (varies by module)
Analog Inputs	Available (varies by module)
Analog Outputs	Available (varies by module)
Number of Modules per Station	Up to 64
Module Width	15 mm, 20 mm, 22.5 mm (depending on module type)