Modbus TCP To RTU Gateway - Novus DigiRail Connect
Communicating With Onboard IO: Standard Mode
DigiRail Connect features built in IO such as relays and transistor outputs which can be operated by Modbus commands. This universal functionality allows it to integrate with many PLCs as a Slave device via Ethernet or RS485. Making it a compact addition to any control system requiring additional IO. This can be valuable when standard OEM parts such as digital input/output cards are in short supply. Depending on the configuration of the DigiRail it can also support analogue inputs and outputs.
Considering the ever rising prices of PLC equipment, adding a small number of additional IO points can sometimes be cost prohibitive. A third party module such as the DigiRail Connect can therefore lower the overall budget for certain projects.
Enabling Gateway Mode: Modbus TCP - Modbus RTU
Another important function of these modules is the Gateway Mode. This allows Modbus RTU (serial devices) to be connected directly to the DigiRail via RS485. With this feature enabled it is then possible to communicate with RTU slave devices via Modbus TCP.
The Gateway Mode is a simple method allowing PLCs with Ethernet to communicate with devices such as temperature controllers, instruments and meters. This is a great solution for networking field devices which are only equipped with RS485 terminals.
Step 1: Configure the Ethernet communications in Nxperience (free config. tool). So you can talk to the PLC on Modbus TCP
Step 2: Check the Gateway option in RS485, enter baud rate etc to match your slave device
Step 3: Make the physical connections - Ethernet from PLC and RS485 from Field Device. In this example with NP785 as slave device
Step 4: Configure the address on your field device (slave). This is important, it needs to be 2 or higher
Sending Modbus TCP Commands Directly To The Module's Built In IO
Sending Modbus TCP Commands To The RTU Device
All Modbus TCP requests received by DigiRail Connect with a different Modbus RTU address than the address configured in the device will be converted to the Modbus RTU protocol and retransmitted in the RS485 network. Responses to these requests will be reconverted to the Modbus TCP protocol and relayed over the Ethernet network to the requesting Modbus TCP client. The Gateway mode adapts the protocol to the physical environment and is transparent to the Modbus TCP client.
No complex mapping is required simply communicate with the RTU device as if it were on the TCP network.
https://www.novusautomation.com/en/product/monitoring-and-data-acquisition/nxperience