Configuring Hardware and Communication Connections STEP 7.pdf

Configuring Global Data Communication
13.2.3 Exceptions for Calculating the GD Circles Required
For S7-300:
Under certain conditions, the number of GD circles required can be reduced:
If an S7-300 CPU ("sender CPU") sends one GD packet only to one other S7-300
CPU ("receiver CPU") only and this receiver CPU sends only one GD packet back
to the sender CPU, only one GD circle is used.
This property reflects the technical data "max. number of receive GD packets per
GD circle = 1."
In the example below you will see from the GD identifier (GD packet number) that
only one GD circle is required.
Example (GD Table After Compiling)
GD Identifier CPU 300 (1) CPU 300 (2)
GD 1.1.1 > MW100 IW2
GD 1.2.1 IW4:3 >MW10:3
For S7-400:
If a maximum of three CPUs exchange GD packets and each of the three CPUs
only sends one GD packet to the other two, only one GD circle is required here
too.
This property reflects the technical data "max. number of receive GD packets per
GD circle = 2."
In the example below you will see from the GD identifier (GD packet number) that
only one GD circle is required.
Example (GD Table After Compiling)
GD Identifier CPU 400 (1) CPU 400 (2) CPU 400 (3)
GD 1.1.1 > MW0 IW0 IW0
GD 1.2.1 IW2 IW2 > MW0
GD 1.3.1 IW0 > MW0 IW2
Configuring Hardware and Communication Connections with STEP 7
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