Programming PLC from a PC through Modbus network


Thread Starter

Razvan Cismileanu


I have a Modbus network with an PLC TSX Unity master, an PLC TSX Unity slave, three PLC Twido slaves and an IBM-PC at Dispatcher provided with Unity software and an SCADA software (Monitor Pro or Vijeo Citect). All the PLCs are provided with Modbus communication module.

The problem is next: how can I transfer the applications through Modbus network from PC Dispatcher to PLCs?

Thank You.

Jerry Miille

II do not understand your configuration from your description. However, our Omnii-Comm module may be able to solve your problem. It can be configured as a data concentrator (using multiple protocols) and connected to a Modbus network. It has up to 5 serial ports and each one can be uniquely configured.

Please contact me at the links supplied on the referenced page.

Thank you.

Razvan Cismileanu

I will repeat my question. I have next network configuration:

1. One PLC Premium Unity with built-in Ethernet communication port. PLC it's linked to the PC where is running a SCADA application.
2. One PLC Premium Unity with built-in Ethernet communication port.
3. Three PLC's Twido with built-in Ethernet communication port which are located in different locations.

All this station (including PC) are linked at a locally Ethernet network (on UNITEL or MODBUS protocol), but link between stations it's a radio link (we don't have yet a frequency allocated).

The customer want to have possibility to program the PLC's through this network.
If you have a solution plese send me an e-mail.
Thank you,

Best regards,

Robert Dusza

At least you have hardware and software from the same manufacturer. You would use the Unity Master to talk to all the slaves from a comm port. The Software would be set up as a Master to another comm port on the Unity Master. The comm port on the Unity Master used to talk to the
SCADA software would be setup as a slave to the PC.

This is all done using the MODBUS drive from the PC to the Unity MASTER. The Unity MASTER would be able to talk MODBUS or a protocol common to the slave hardware.

I don't know much about the Schneider hardware or software, but my experience tells me to that the above scenario is possible. You need to check the manuals and talk to the rep about.


Robert J. Dusza, Jr.
Project & Technical Support Manager
(V) 1-860-647-3219
(F) 1-860-647-3150
E-mail - [email protected]
Manchester Water & Sewer Dept.
125 Spring St. P.O. Box 191
Manchester, CT 06045-0191
I can't say for Twido nor for Citect, I have not use any of them yet.

Once, you have configured the IP addresses of the Unity PLC, you can program them through TCP/IP network using Unity Pro. In Unity Pro, you may define PLC address as TCP/IP and type in the IP address of the PLC you want to talk with.

You can also program the SCADA through your TCP/IP network if it is a Monitor (or Factory Link, it is the same product). It is a little bit more difficult but quite useful if you got several supervisory systems and need to save money (only one build time licence is needed) or need to rollout the same applications into them fastly (make all modifications with one PC and modify all the others from the same PC).

Tomy Zacharia

Without knowing anything about Unity or Twido PLCs, programming 'should be' possible if end-to-end Ethernet link is available i.e. from PC having the programming software to the remote slaves.

The element of surprise remains, as many PLCs cannot be programmed in run-mode, cannot simultaneously scan io and be programmed etc. etc.

I say 'should be' possible as Modbus uses a specific tcp/udp port and consequently programming would be done through a different tcp/udp port.

How do you usually program the remote PLCs? Are the remote PLCs programmable over Ethernet? RTFM!!

Tomy Zacharia

Chris Goossens

There is no difference between passing data from a PC to a PLC in Eternet TCPIP (Modbus) or programming a PLC using the same hardware. If a SCADA runs on a PC and gets data from PLCs. You must be able to program the PLCs using the same hardware.
I'm not familiar with the TSX line but I have been deploying a Modicon Quantum / Momentum network in my plant. All of our procs come with a Modbus+ port as well as a Modbus port. All procs are on a Modbus+ drop. We hook HMIs to the Modbus port. I can modify/develop code from my office as that's where the network originates. For me to modify/develop code through Modbus, I have to physically go out to the proc and plug a DB-9 into the modbus port of the proc. I'm not aware of any way to "network" a staight-up Modbus line. Also since Modbus is a 9600 baud "232" serial connection distance will become a real problem after about 75'. I grabbed a TSX catalog from the Schneider website (MKTED204012EN.pdf), and it looks like you can get Modbus plus modules for the TSX line.

But if you already have everything on ethernet, couldn't you drop in a standard switch to tie all the systems together so you can access all PLCs from your development station?