Applies To:
  • CitectSCADA 5.xx, 6.00
  • CitectHMI 5.xx, 6.00

I have a TSX37-21 Micro PLC that I would like to communicate with Citect. The only ports the TSX Micro has is a TER, and AUX port. I know that Citect's UNITEL driver is capable of communicating with the TSX Micro, but I do not have a DS300 card for the PC. What other options do I have for setting up communications?

The most cost effective solution is to use the TSX Micro's programming cable (TSX-PCX-1031), along with the Modbus protocol. The TER and AUX port is physically the same port. The AUX port is usually used for HMI units via a protocol that supports multidropping (Unitelway). At the time of writing this KB, not all TSX Micro PLC's supported the Modbus slave protocol on their TER port. Check with the manufacturer for details of your TSX Micro PLC's TER port capability. Below is a description of how to establish communications with a TSX37-21 Micro PLC:

1) Configure the TER port as a Modbus Slave. Note down the Slave address, Transmission speed, Parity and Stop bits as these will become important in the Citect configuration.

2) Download this configuration to the PLC using the TSX-PCX-1031 programming cable. It is important to have the mode dial on the cable set to TER direct (mode 0).

3) The next step is to configure the Citect Project with the Modbus I/O Device Communication settings. You can run the computer setup wizard, and select a modbus RTU device:

Complete the communications wizard, entering in the appropriate device address. You may need to manually change the Port form Baud Rate to match the PLC transmission speed. Below is the Boards, Ports and I/O Device forms:

4) The next step is to configure some variable tags to read data from the PLC. The only PLC address ranges supported by the Modbus protocol when communicating with the TSX Micro is %M and %MW.

Here is the TSX Micro to Modbus address conversion:
PLC address Modbus Address
%M0 = 000001
%MW0 = 400001

5) The next step is to pack, and compile your project.

6) Now set the programming cable (TSX-PCX-1031) dial to mode 3. This enables the TER port to communicate using the configured modbus protocol. When you set it to Mode 0 (TER direct) it over-rides the port configuration, so you can then use UNITELWAY and the PL7 Pro software for programming the PLC.

Note: You cannot communicate to the PLC with Citect and PL7 Pro at the same time. Since Citect will be using Modbus, and PL7 Pro will be using UNITELWAY.

7) Start Citect runtime, and confirm that you have successful communications.


TSX37, Micro, Modbus, Programming Cable