Vaisala’s viewLinc Enterprise Server software supports measurement data acquisition from Modbus TCP and RTU devices. This technical note describes methods that will allow Modbus devices to communicate with viewLinc. Adding a Modbus device to viewLinc involves two steps: first establish communication between viewLinc and the device, and then define the device in viewLinc.
| Establishing communication | Modbus TCP | Modbus RTU |
|---|---|---|
| The connection process differs depending on whether the device is Modbus TCP or Modbus RTU. | Modbus TCP devices communicate over Ethernet. Turn on the Modbus device and connect it to the same network as your viewLinc server. Follow the steps on page two to define the device in viewLinc. | Modbus RTU devices communicate serially (typically over RS-485). In order to establish communication between a Modbus RTU device and your viewLinc server, the Modbus device needs to be connected to the network by an Ethernet-to-serial adapter device. Vaisala recommends using a Digi Portserver TS device for this purpose. |
Connecting RTU Modbus Devices
In order to connect the Modbus device to a Digi Portserver, you need a cable with appropriate connectors. The Digi Portserver TS uses an RJ45 connector with the pinout below (Source: PortServer® TS Family Quick Start Guide). The pinout on the Modbus device’s side will depend on the connectors available on that device. Please refer to the manufacturer’s documentation for specifications. Different Modbus RTU devices may require different settings or connections, depending on the model and adapter required. Always ensure the device is connected and communicating properly before proceeding.
Review serial pinouts
The following table shows the pin positions for connecting serial devices using either 10-wire or 8-wire connectors.
| Pin positions for connecting serial devices | ||
|---|---|---|
| PortServer TS products use an RJ-45 10-wire jack (female), with Pin 1 in the following location. | For a 10-wire connector, Pin 1 of the connetor is shown here. | For an 8-wire connector, connect the pins to the center 8 pins of the 10-wire jack. |
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The following table lists the serial port pin assignments for different connector types.
| Serial port pin assignments | ||||||
|---|---|---|---|---|---|---|
| Pin # on 10-wire connector | Pin # on 8 wire connector | EIA-232 | MEI versions only | |||
| EIA-422/485 Full-duplex | EIA-485 Half-duplex | |||||
| 1 | RI | TxD- | N/A | |||
| 2 | 1 | DSR* | RxD- | DATA- | ||
| 3 | 2 | RTS | RTS+ | N/A | ||
| 4 | 3 | CGND | CGND | CGND | ||
| 5 | 4 | TxD | TxD+ | N/A | ||
| 6 | 5 | RxD | RxD+ | DATA+ | ||
| 7 | 6 | SGND | SGND | SGND | ||
| 8 | 7 | CTS | CTS+ | N/A | ||
| 9 | 8 | DTR | RTS- | N/A | ||
| 10 | DCD | CTS- | N/A | |||
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* Use the Altpin setting to swap these two signals.
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