Configuring Hardware and Communication Connections STEP 7.pdf

Configuring Global Data Communication
Data Transfer Process
Global data communication functions according to the broadcast method, meaning
the receipt of the global data is not acknowledged. The sender does not receive
information as to whether a receiver and which receiver has received the sent
global data. If the process requires secure data exchange, use another service
such as S7 functions.
Subnets for Global Data Communication
GD communication is possible:
• Via an MPI subnet only (between different stations) or
• Via the backplane bus only (for example, between S7 CPUs in a rack in
multicomputing)
How Does an Address Area Become a Send/Receive Area?
The address areas that are involved in global data communication are configured
in a global data table (GD table) using STEP 7:
• Every column is assigned to exactly one CPU which means the columns
represent the CPUs involved in the data exchange (maximum 15 CPUs)
• Every row (or more exactly: every cell that can be edited in a row) represents
the address areas via which one CPU only sends and one or more CPUs
receive
When you have filled out the table, compiled it, and downloaded it to the CPUs
involved, these CPUs send and receive cyclically via these address areas at the
scan cycle checkpoint (meaning at the time at which the process image update
takes place).
Special Feature: With the S7-400, configured global data can also be sent using
SFC60 (GD_SND) for event-driven sending and received using SFC61 (GD_RCV).
Configuring Hardware and Communication Connections with STEP 7
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