4.2 DXM Master Configuration
The DXM Controller operates as a Modbus master device, use the DXM Configuration Tool to configure read or write
operations of the DXM Modbus network. The DXM Controller communicates with all internal and external peripheral devices
using the external Modbus bus RS-485 (M+, M-)
There are four internal Modbus slave devices that are configured from the factory with slave IDs. Assign slave IDs of 2
through 10 to Modbus slave devices that are physically wired to the DXM Controller. Assign slave IDs or 11 through 60 to
wireless slaves within the MultiHop network.
Do not assign a slave ID of greater than 10 to Modbus slave devices that are physically wired using the RS-485 port if
there is an internal MultiHop ISM radio in the DXM Controller. The MultiHop ISM radio attempts to send any Modbus data
intended for slaves 11–60 across the radio network, which conflicts with wired slave devices if the slave IDs overlap. The
MultiHop master radio can be changed from the factory default of 11–60 Modbus slave IDs if more hardwired slaves are
required.
4.3 Modbus Operation
All Modbus transactions are managed by a central Modbus engine. If there are Modbus messages intended for a Modbus
slave that doesn't exist, the Modbus engine waits for a response until the timeout period is expired. This slows down the
Modbus polling loop for read and write operations. For this reason, verify all Modbus read and write operations are
intended for Modbus slave devices that are in the network.
If a Modbus slave is not in the network, either a wired or wireless device, the operation of the LCD menu system can be
compromised. Operations like Binding, Site Survey, or accessing the ISM menu may be slower. This is because all internal
devices of the DXM Controller are also Modbus slaves, ISM radio, I/O base board, LCD, and internal Local registers.
4.4 Wireless and Wired Devices
4.4 Wireless DX80 Gateway
The DX80 Gateway architecture is a star architecture in which all Nodes in the system send their data back to the
Gateway. The host can access the entire network data from the Gateway, which is Modbus slave ID 1.
Because the DXM Controller will not be sending any Modbus messages across the wireless link, the timeout parameter can
be set low (less than 1 second) and it is treated like a directly connected device.
4.4 MultiHop Master
The MultiHop master radio forms a wireless tree network using repeaters and slave devices. Each device in a MultiHop
network must be assigned a unique Modbus Slave ID and is accessed as a separate device.
For the DXM Controller to talk with a MultiHop device in the wireless network, the master MultiHop device interrogates
every message on the RS-485 bus. If they are within the wireless devices range (slave IDs 11 though 60), the message is
sent across the wireless network. To change this range, the user must adjust the offset and range setting in the MultiHop
master radio (Modbus Slave ID 1). Modbus register 6502 holds the Modbus offset, default 11. Modbus register 6503 holds
the number of Modbus slaves allowed (maximum of 100).
Modbus Slave ID
Description
1
Allocated for the internal ISM radio device, either a DX80 Gateway or MultiHop Master
2–10
Slave addresses available for direct connected Modbus slave devices to the master RS485 port (M+ , M-)
11–60
Allocated for wireless MultiHop radio network devices. If there is not an internal MultiHop in the DXM Controller, these slave
addresses are available to use for directly connected devices.
61–198
Available to user for direct connected Modbus slave devices or the expansion of the wireless network slave IDs to go past 50
wireless devices.
199
Allocated for internal Local Register
200
Allocated for the I/O base board, will be different for special DXM slave only models.
201
Allocated for the LCD display board, the user can read/write LEDs.
DXM100 Controller Instruction Manual
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