Instructions

UM-0085-B09 DT80 Range User Manual Page 362
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Host RS232 Port
The host RS232 port can also be used for controlling a Modbus sensor. This is configured in a similar way:
PROFILE HOST_PORT FUNCTION=MODBUS_MASTER
Note that because RS232 is a point-to-point connection, only one Modbus device can be connected to this port.
As with the serial sensor port, you may need to change the configured baud rate or other settings. For more details on
setting up the port and the possible wiring configurations, see Host RS-232 Port (P195).
USB Port
The USB port may also be used for polling a Modbus sensor. Such a "sensor" would generally be a PC-based system,
as a stand-alone sensor would most likely have the wrong type of USB interface and would not be able to connect to the
DT80's USB port.
To configure the DT80 USB port for Modbus master operation use:
PROFILE USB_PORT FUNCTION=MODBUS_MASTER
For more details, see USB Port (P187).
Connecting Network Modbus Sensors
A network Modbus sensor communicates with a client system such as the DT80 using a TCP/IP network. This network
may use a variety of different physical link types, including Ethernet, serial links, wireless and optical fibre. Normally, the
DT80's Ethernet port is used to connect to a TCP/IP network, and in most cases the sensor will also connect using an
Ethernet port.
In order to communicate over a TCP/IP network, all devices connected to that network are required to have a unique IP
address. So in order for the DT80 to be able to poll network Modbus sensors, the DT80 must have an IP address and so
must each sensor.
See Ethernet Communications (P231) for more details about IP addresses and how to assign one to the DT80.
There are many different ways in which network Modbus sensors can be connected to the DT80. The simplest possible
network is a single cross-over cable between the sensor and the DT80's Ethernet port.
Figure 166: Direct Ethernet connection between DT80 and a network Modbus sensor
More typically, the DT80's Ethernet port would be connected to an existing Ethernet network, which may have several
Modbus devices attached. There may even be devices connected via the Internet.
Figure 167: One possible Modbus network configuration
For example, Figure 154 shows one possible network configuration. In this example, three network Modbus sensor
devices are used. Two are connected to the local Ethernet network, and one is remote, accessed via the Internet. DT80
#2 is also set up as a network Modbus sensor, as described in Modbus Interface (P175). All of these devices operate as
Modbus server, or slave, devices.