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Functions
5.2 Intelligent IO devices (I-devices)
PROFINET with STEP 7
138
Function Manual, 05/2021, A5E03444486-AL
Note
Special characteristic during startup of the higher-level IO controller
In contrast to the station return message from IO devices in the IO controller, which are
covered completely by the call of the OB 86, the station return message of a higher-level IO
controller in the I-device is separated into 2 parts:
1.
Call of the OB 86: The initial values for the outputs of the I-device are set. However, the
input values are not yet valid. These values will first be valid with the opening of OB 86 in
the higher-level IO controller.
2. Call of OB 83 for each input transfer area; with this call, the validity of an input transfer area
is displayed. The starting up of the I device is first complete when the OB 83 has been called
for the input transfer areas. This step can be delayed or not occur at all in the following
situations:
– Higher-level IO controller is in STOP: OB 83 is first called at the STOP-RUN transition of
the higher-level IO controller.
– The IRT communication has been disrupted (sync-master failure, topology error, ...).
OB 83 is opened only after the IRT communication has taken place.
Reference
For more information on error handling in the case of direct I/O access, refer to "Error
handling" in the STEP 7 online help.
5.2.8 Rules for the Topology of a PROFINET IO System with I-Device
Introduction
The following recommendations for the structure and configuration of an IO system when
using I-devices will help you to keep the bandwidths required for keeping communication
small.
The following communication paths should not overlap:
•
Communication paths between the IO controller and the IO device of its IO system.
• Communication paths of the I-device CPU and the IO devices of your IO system.