Modbus RTU
The DXM manages two separate physical ports running the Modbus RTU protocol. The DXM is the Modbus Master
when operating the Modbus master RTU port. The DXM uses the master Modbus RTU bus to communicate with
locally connected Modbus devices or uses the Banner wireless radio to communicate with remote Modbus devices.
The other Modbus RTU port is used by a host system to access the DXM as a slave device. The slave Modbus RTU
port allows access all the internal registers concurrently with the master RTU port. Set the slave Modbus ID using
the LCD menu:
SYSTEM CONFIG
>
DXM Modbus ID
.
By default, the Modbus RTU ports are active. Configure the port parameters using the configuration software.
Modbus TCP/IP
A host system acting as a Modbus master can access the DXM using the Modbus TCP/IP protocol over Ethernet.
Standard Modbus port 502 is used by the DXM for all Modbus TCP/IP requests.
All internal registers are available to the host system concurrently with Modbus RTU.
By default, Modbus TCP/IP is active. Configure the DXM using Modbus TCP rules in the configuration software.
EtherNet/IP
™
The Ethernet port is actively running EtherNet/IP. From the factory the DXM is configured to read and write registers
on DX80 wireless devices 1 through 16. Custom configurations can be set using the configuration software.
By default, EtherNet/IP is active.
1.3 DXM Modbus Overview
The DXM700 uses internal 32-bit registers to store information. The processor's internal Local Registers serve as the main
global pool of registers and are used as the common data exchange mechanism. External Modbus device registers can be
read into the Local Registers or written from the local data registers.
The DXM700, as a Modbus master device or slave device, exchanges data using the Local Registers. Modbus over Ethernet
(Modbus/TCP) uses the Local Registers as the accessible register data.
Using Action, Read/Write, and Threshold Rules allows you to manipulate the processor's Local Registers. The ScriptBasic
programming capabilities extends the use of Local Registers with variables to create a flexible programming solution for more
complex applications.
The processor's Local Registers are divided into three different types: integer, floating point, and non-volatile. When using
Local Registers internally, the user can store 32-bit numbers. Using Local Registers with external Modbus devices follows the
Modbus standard of a 16-bit holding register. Local Registers are accessible as Modbus ID 199.
Accessing the I/O Base and the LCD follows the same communication as an external Modbus device. Each device has an ID
number to uniquely identify itself. The I/O base is Modbus ID 203 and the LCD is Modbus ID 201.
Figure 4. DXM700 Modbus overview
Ethernet
RS-232
RS-485 (master)
RS-485 (slave)
USB
Local Registers
(Modbus ID 199)
Processor/Outputs (Base Board)
Outputs (Modbus ID 203)
Processor Controlled
Modbus Data Traffic
Control
Cellular Modem
Outputs
Local Registers
Non-Volatile
Local Registers
Float
Local Registers
Integer
ISM Radio (Modbus ID 1)
User Display (Modbus ID 201)
Gateway or MultiHop
LED / LCD Display
Sure Cross
®
DXM700-Bx Wireless Controller
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