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Device Addressing and Message Routing
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If a match is not found in the table, conversion proceeds as in Figure 7.
If the address is in the range 1 ... 64 (Direct Attach Address), the
message is routed to the specific node address 1 ... 64 on the local
Modbus Plus network.
If the address is in the range 71 ... 74 (MUX Attach Address), the
message is routed to a single device at one of the local Modbus ports.
Addresses 71 ... 74 specify ports 1 ... 4, respectively.
If the address is in the range 80 ... 255 (Implicit Attach Address), it will
be divided by 10 within the BM85. The quotient and remainder of the
division will become the first two bytes of the five-byte routing path.
This method allows two levels of Modbus Plus addressing: the quotient
byte specifies a Bridge Plus address on the local network, and the
remainder byte specifies the destination node on the second network.
The final three bytes in the routing path will always be zeros.
Silent Master Port Addressing
A Modbus port can be configured as a Silent Master network port. In
this configuration, one Modbus master device and one or more slave
devices can be connected to the port. The master device can address its
own network's slave devices directly. It can also address devices at other
ports on the same BM85, or devices across Modbus Plus.
Special considerations are needed for addressing in this configuration.
The intent is to avoid address conflicts between slave addresses at the
local port and other addresses that may exist elsewhere.
The slave devices on the Silent Master port must have unique addresses.
They must not be the same as a node address (1 ... 64) on the BM85's
local Modbus Plus network. They must also not exist as entries in the
address mapping table stored within the BM85. The Modbus addresses
in the master's queries to the slave devices must not map beyond the
Silent Master port -- neither to any routing on Modbus Plus, nor to
another port on the BM85.
Note:ąReserved addresses are not to be used in user applications.
When the port is configured as a Master port, addresses 65 ... 70 and
75 ... 79 are reserved. Addresses 71 ... 74 are available for use.
When the port is configured as a Silent Master port, addresses 65 ... 79
are reserved.
The Bridge Multiplexer will respond with a Modbus exception response
to any message addressed to a reserved address.