Configuring Hardware and Communication Connections STEP 7.pdf

13 Configuring Global Data Communication
13.1 Overview: Global Data Communication
Introduction
Global data communication (GD communication) is a simple method of
communication integrated in the operating system of the S7-300 and S7-400
CPUs.
GD communication allows the cyclic exchange of data between CPUs via the
multipoint interface. Cyclic data exchange takes place with the normal process
image.
Global data communication is configured with STEP 7; transferring global data is
done by the system and is not therefore programmed.
The following sections show how you can estimate using the technical
specifications as given for every CPU (number of GD circles, size and number of
GD packets etc.) what quantities of data can be exchanged between CPUs using
the "GD communication" process.
The following are also listed:
• Send and receive conditions to be observed
• The formula for estimating the approximate response time
What Are Global Data?
Global data as they are used in the GD communication process are the following
address areas in the CPU:
• Inputs, outputs (from the process image)
• Bit memory
• Data block areas
• Timers, counters (not recommended because the values are no longer current
at the receiver; can only be configured as send address areas)
Peripheral areas (PI and PQ) and local data cannot be used for global data
communication.
Configuring Hardware and Communication Connections with STEP 7
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