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Cooper Bussmann 915U-2 Wireless Mesh I/O and Gateway User Manual
57
Rev Version 1.2.2
Each serial port can be configured to operate in one of the following operating modes:
•
Modbus RTU Master
—This mode should be configured when the port is operating as a Modbus master, for
example, when Modbus RTU slave devices are connected directly to the serial port.
•
Modbus RTU Slave
—This operating mode should be used when the port is being used as a Modbus RTU
slave, for example, when a Modbus master (such as DCS, or SCADA) is connected to the serial port.
•
Expansion I/O
—This operating mode should be selected when ELPRO serial expansion modules are
connected to the module.
Modbus RTU Master
To configure a module serial port as a Modbus RTU master, click the serial port (
RS-485
or
RS-232
) in the project
tree, and then select
Modbus RTU Master
from the
Operating Mode
drop down menu (see Figure 55).
The Modbus RTU master should be configured if the 915U-2 is acting as a Modbus RTU master and polling
Modbus slave devices via the selected serial port. It also allows Ethernet Modbus/TCP clients connected to the
915U-2 Ethernet port to communicate with Modbus RTU slave devices connected to the configured serial port.
The 915U-2 makes this possible by internally performing the necessary protocol conversion. The conversion is
performed by the 915U-2 that is directly connected to the Modbus serial device (only this module needs to have
Modbus TCP to RTU gateway enabled).
Figure 55 Modbus TCP/RTU
When a serial port is configured as a Modbus RTU master there are a number of parameters (such as baud rate,
data format and flow control) that can be adjusted depending on the devices connected.
Port Number
TCP Port number configured for the serial port. A standard port number will be
assigned, depending on the port. An RS-232 port is assigned 503, and an RS-485
port is assigned 504. Generally, these port numbers only need to be changed if the
TSP client is using a non-standard port number.
Request Pause
Delay between serial requests, in milliseconds.
Response Wait
Serial response timeout period, in milliseconds. A serial retry is sent if a response is
not received within this timeout period.