Modbus to Ethernet Bridge
Figure 3 shows an example of message address mapping between a Modbus Master and a Modbus Slave using two Bridges with an Ethernet link.
Figure 3 Mapping Modbus and IP Addresses
Modbus
Master
Ethernet
192.168.001.024
Modbus message to Slave address 10
Bridge
B
Bridge
A
Modbus ± IP Address
Mapping Entry:
010 : 192.168.001.024
Modbus
Slave(s)
Bridge routes message to Slave
according to user±defined setup:
Message Slave Address (10)
or
Fixed Slave Address (1 ... 247)
These are the events in the message routing:
HThe Modbus Master sends its message containing address 10 decimal to Bridge A.
HYou have set an entry in the mapping table in Bridge A. Your entry specifies that messages with address 10 are to be mapped to IP address 192.168.001.024.
HBridge B has that IP address and receives the message.
HDepending on the option you set in Bridge B, the message is routed either to the Modbus Slave device at address 10 as specified in the message, or to a fixed Slave address in the range 1 ... 247.
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