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Functions and applications
June 2023
9.2
Redundant Com Card communication
For the redundancy two Com Cards, installed into the AMS 6500 ATG system, are
required . The following communication interfaces are redundant:
•
RS 485 interface for communication between cards and Com Card
•
Modbus over TCP/IP communication
•
Modbus over RTU communication (salve interface)
•
OPC UA
Both communication cards are interconnected by the backplane. The primary master card
(left slot) operates as the master on the RS 485 bus. The secondary master card is passive
on the RS 485 bus. The primary master card collects the data from all connected cards.
The data is mirrored to the secondary, passive card. Both Com Cards provides the data
through the Modbus and OPC UA interfaces. If the primary master card fails then the
secondary master card becomes the master on the RS 485 bus and takes over the
communication with the connected cards. There are different redundant Modbus
communication setups:
9.2.1
Modbus RTU - Both cards with an identical device
address
Figure 9-1
•
Single Modbus RTU connection to the control system.
•
Both Com Cards have an identical device address.
Only active card responses is selected for parameter Modbus RTU → Serial Modbus
mode.
•
The primary master provides Modbus RTU data.
•
Bus termination at primary master
•
Bias activated at primary master
•
If the primary master fails, the secondary master becomes active and provides Modbus
data. The bus termination and the bias are automatically activated at the secondary
master.
54
shows a connection overview of a redundant Modbus RTU. Function:
Operating Manual
MHM-97875
MHM-97875, Rev. 5.15
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