Ignition to Unitronics Vision 530 OPLC via MODBUS

[KP_EENG]

Has anyone been able to get Inductive Automation's Ignition MODBUS OPC Server to communicate with a Unitronics Vision 530 OPLC? I can get Ignition to talk with a Wago 750-871 via MODBUS with no problem, but I can't get Ignition to talk with the UNITRONICS. I have been in contact with Ignition Tech Support and Unitronics Tech Support, but no luck so far. I was hoping that someone on this forum has been able to do this and can offer some suggestions.

Regards

 

[danw]

Can you talk to the Unitronics and get a response with a generic Modbus master like Simply Modbus, Modpoll or Modscan32?

 

[KP_EENG]

Actually, I can talk to the Unitronics with Wonderware's MODBUS OPC server.

 

[danw]

Wonderware OPC server talks to Unitronics via Modbus/TCP.

Ignition OPC server talks to Wago via Modbus/TCP.

But Ignition OPC server will not talk to Unitronics via Modbus/TCP.

>I can't get Ignition to talk with the UNITRONICS.

Does that mean that you can't see any response from the Unitronics? nothing at all?

 

[KP_EENG]

Does that mean that you can't see any response from the Unitronics? nothing at all?

Not exactly. I have figured out that the Unitronics has a difficult time with Wonderware and Ignition hitting it at the same time. If I disable the Wonderware DA Server, the Ignition server does connect to the Unitronics, but I can't browse any tags. My suspicion is that there is a configuration setting with the Ignition OPC Server or something with the Unitronics hardware configuration that I am missing. I was hoping that someone here may have been able to get Ignition and a Unitronics PLC talking.

Regards

 

[danw]

There is Modbus/TCP and then there is Modbus/RTU over ethernet, and the difference is not well defined, but I've concluded that one attribute of Modbus/RTU over ethernet is the Modbus RTU limitation of one master only.

Some industrial devices (single loop controllers in particular) are really Modbus/RTU over ethernet because they choke and cannot handle more than one master as evidenced by polling messages arriving too close to one another.

I wonder if the Unitronics slave side can handle multiple masters?

Have you asked Unitronics if they have tested and know whether the Modbus slave side can handle multiple masters (not that you'd get an informed answer . . .)?

 

[KP_EENG]

Apparently, Unitronics does have a difficult time handeling more than one master, although they do have the capability of configuring different channels, which I have not played around with yet. Regardless, I finally got the Unitronics to communicate. The Wago configuration required a Slave ID of 0, which is what I was using for the Unitronics. After using the Simply MODBUS TCP utility that you suggested, I noticed that I had to set the Slave ID to 1 in order for the device to communicate. I changed the ID to 1 in the Ignition MODBUS address configuration and Ignition went online with the Unitronics.

Thanks for the suggestion to use Simply MODBUS. It really helped in this situation.

Best regards,

 

[KP_EENG]

I spoke with the Unitronics technical support today and they provided me with a program that allows me to configure one TCP socket with port number 502 and another TCP socket with port number 20257 and this allows the OPLC to talk to Wonderware and Ignition at the same time. Unfortunately, these ports only allow me to monitor data from the Unitronics and not write data to it. I just thought that I would provide this update for anyone who is interested in the future.

Regards

 

[robertkjonesjr]

Unfortunately, these ports only allow me to monitor data from the Unitronics and not write data to it.

Do they not support the write function codes 6, 16, 23, etc? Do you know what the write restriction is?

 

[KP_EENG]

The way that I understand from reading the Unitronics communications manual is that the Vision 530 Ethernet card is capable of four sockets. Socket 0 can be set for MODBUS UDP which allows Read/Write data. Socket 1 is for communication with the PC Programming tool and Sockets 2 and 3 are used for Read Only MODBUS communications with SCADA systems or other PLCs.

I have been able to use sockets 2 and 3, but I have not been able to get socket 0 to work for read/write purposes. I will try later when I have more time.

Regards

 

[danw]

Thanks for the follow-ups.

UDP is an alternative to TCP/IP. It is broadcast only, not point-to-point. I wouldn't spend any time trying socket 0 because it won't work with your TCP/IP ethernet functions.

If Unitronics says that their registers are read-only, then they're read only. There's no Modbus master instruction that can force a slave to accept a write to a slave's register when that slave's designer has designated it a read-only register.

 

[robertkjonesjr]

UDP is an alternative to TCP/IP. It is broadcast only, not point-to-point. I wouldn't spend any time trying socket 0 because it won't work with your TCP/IP ethernet functions.

UDP is very often Unicast - point-to-point. You can make it broadcast, but that doesn't mean it has to be. Here is a discussion on how to do broadcast over at the Unitronics forum:

A Wireshark trace would show what is actually happening. Also the sockets are selectable - the default might be as indicated, but you can change them in code.

If Unitronics says that their registers are read-only, then they're read only. There's no Modbus master instruction that can force a slave to accept a write to a slave's register when that slave's designer has designated it a read-only register.

I agree this is generally true, but I would have to wonder about Modbus compliance? I have no trouble writing to my Unitronics V350 from a Redlion G3 panel to control my lawn sprinkler using ModbusTCP.

Can someone try the write and capture the event in Wireshark? That would tell exactly how the Modbus write is handled, based on the error returned.

 

[cjd1965]

I have no trouble writing to my Unitronics V350 from a Redlion G3 panel to control my lawn sprinkler using ModbusTCP.

You must have a lot of lawn to do this

 

[cjd1965]

S7 Graph - Timer

deleted by cjd1965

 

[robertkjonesjr]

You must have a lot of lawn to do this

Didn't you know that home projects are not constrained by such issues as Return on Investment, cost savings, yield improvements, progress reports to management...

I act as gatekeeper / project manager / programmer / panel builder / buyer / troubleshooter / executive management all at the same time. The speed at which 'we' can make decisions is amazing when it is a one-man show!