
Pin
Parameter
Description
Pin 10
RS-232 Rx
Pin 11
Secondary RS-485 –
or RS-232 RXDY
Select using the RS-485 and RS-232 Selection Jumpers (see
•
In position "a" these pins are a secondary RS-485 bus. The DXM is a Modbus slave on
this bus.
•
In position "b" these pins are the flow control signals for the RS-232 signal on pins 9 and
10.
Pin 12
Secondary RS-485 +
or RS-232 TXRDY
5.11 Modbus RTU Master and Slave Ports
The DXM can be a Modbus RTU master device to other slave devices and can be a Modbus slave device to another Modbus
RTU master. The DXM uses the primary RS-485 port (M+/M-) as a Modbus RTU master to control external slave devices. All
wired devices connected to the master RS-485 port must be slave devices. The secondary port (S+/S-) is the Modbus RTU
slave connection.
•
As a Modbus RTU master device, the DXM controls external slaves connected to the primary RS-485 port, the local
ISM radio, local I/O base board, and the local display board.
•
As a Modbus RTU slave device, the DXM local registers can be read from or written to by another Modbus RTU
master device.
The secondary (slave) Modbus RS-485 port (S+/S-) is controlled by another Modbus master device, not the DXM. The slave
port is used by an external Modbus master device that will access the DXM as a Modbus slave device.
Use the configuration software to define operational settings for both the Modbus RTU master port and the Modbus RTU
slave port.
Set the Modbus Slave ID for the secondary RS-485 port using the LCD display menu:
System
>
DXM Slave ID
.
5.11.1 Modbus Master and Slave Port Settings
The basic communications parameters for the RS-485 ports are set in the DXM Configuration Software and are saved in the
XML configuration file. All basic settings are available under
Settings
>
System
screen.
Master port parameters include:
•
Baud rate
and
parity
•
Set the
Communications Timeout
parameter to cover the expected time for messages to be sent throughout the
wireless network. For the DXM, the
Communications Timeout
parameter is the maximum amount of time the DXM
should wait after a request is sent until the response message is received from the Modbus slave device.
•
Maximum Polling Rate
sets the minimum wait time from the end of a Modbus transaction to the beginning of the
next Modbus transaction.
Figure 20. Settings > General screen
The Modbus Slave port settings include:
Sure Cross
®
DXM150 and 1500-Bx Wireless Controllers
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