How to connect 10 RS-485 Devices with Citect SCADA


Thread Starter


Hi Guys

can anyone help me to implement SCADA system for 10 devices that can communicate via rs-485 (MODBUS-RTU).... I need a hardware and software help.

thank you :)

Patrick Lansdorf

Hi Amer,

Normally, you will need a gateway (Modbus RTU to Modbus TCP), where the Scada will be the Modbus TCP master and the gateway is a Modbus TCP slave to Modbus RTU master.

There are 2 types of gateways, transparent and non-transparent.
When using a transparent Modbus gateway, the Modbus TCP master sends a Modbus TCP command, with Modbus RTU ID enclosed, and the gateway will simply translate the Modbus TCP command to a Modbus RTU command, using the enclosed Modbus RTU ID.

A non-transparent Modbus gateway, is pre-configured to read/write to Modbus RTU slave(s) and has one read/write area, where the Modbus TCP master can access the data.

1. Ensure that your Scada has Modbus TCP master capabilities.
2. Once 1. is confirmed, see if the master can use a transparent gateway, meaning capable of adding Modbus RTU Slave ID in the Modbus TCP message.
3. Get a transparent Modbus gateway. There are plenty of vendors, since I work for HMS, I will recommend the Anybus Modbus RTU to TCP Gateway.

My 2 cents

Patrick L
I am assuming that your SCADA is running on a PC. RS-485 allows you to Daisy chain devices; so you can create a string of your 10 devices, then connect them to your PC using a converter like our USB to RS-485 converter:

The USB connection will appear as a Com port on your PC. Using this Com port, you can use the Modbus driver in your SCADA software to poll data from each device.

Note: Each device must have a unique Modbus ID