DXM Master Configuration
—When the DXM operates as a Modbus master device, use the configuration software to
configure read or write operations of the DXM Modbus network. The DXM 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. 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. 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.
7.2 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 (such as the ISM radio, LCD, etc) of the DXM700 are also Modbus slaves.
7.3 Wireless and Wired Devices
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 will not be sending any Modbus messages across the wireless link, the timeout parameter can be set low
(less than 1 second) and the device is treated like a directly connected device.
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 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).
Table 20: Modbus Slave IDs for wireless and wired devices
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 DXM700, 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.
7.4 Modbus Communication Timeouts
A Modbus timeout is the amount of time a Modbus slave is given to return an acknowledgment of a message sent by the
Modbus master. If the Modbus master waits for the timeout period and no response is seen, the Modbus master considers it
a lost message and continues on to the next operation.
The timeout parameter is simple to set for Modbus devices directly connected to the DXM700, if there are no MultiHop
wireless devices. Special considerations need to be made to set the timeout parameter when a MultiHop network uses the
DXM700 as the master radio.
Configure controllers operating wireless networks to allow for enough time for hardware transmission retries. Set the
Communications Timeout
parameter to cover the expected time for messages to be sent throughout the wireless network.
For the DXM700, the
Communications Timeout
parameter is the maximum amount of time the DXM700 should wait after a
Sure Cross
®
DXM700-Bx Wireless Controller
44
www.bannerengineering.com - Tel: + 1 888 373 6767
