User`s manual

MGate MB3000 User’s Manual Configuring the Modbus Gateway
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Set up Slave ID Mapping (Smart Routing)
The Slave ID Map tab is where slave IDs are managed. The definitions on this tab determine how
requests will be routed by the unit.
How Slave IDs are Mapped on the MGate MB3000
When a Modbus master requests information from a Modbus slave, the request is addressed to the
desired slave's ID, which must be unique on the network. When Modbus networks are integrated by
a Modbus gateway, complications can arise if the same slave ID is being used on different networks.
If this is not properly addressed, a request sent to that slave ID would receive more than one response,
causing communication problems.
With the MGate MB3000, this situation is addressed by using a slave ID map. While configuring the
MGate, users set up a range of "virtual" slave IDs that are mapped to slave devices on a specific
Modbus network. To send a request to a slave that is on a different Modbus network, a master would
address the request to the appropriate virtual slave ID. The MGate then routes that request as
specified by the slave ID map.
For example, if a TCP master needs information from an ASCII slave, it addresses the request to the
corresponding virtual slave ID as defined on the MGate's slave ID map. The MGate identifies the
request as within its virtual slave ID range and forwards the request to the Modbus ASCII network,
this time addressed to the device's actual slave ID.
Virtual slave IDs must not conflict with each other or with other TCP slave IDs.
ATTENTION
The MGate MB3000 will disregard any request that is not addressed to a virtual slave ID on its
slave ID map. If a device has not been assigned a virtual slave ID, it will not be accessible by
masters on the other side of the Modbus gateway.