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how do i configure my PLC for dual ModbusTCP Slave.


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I want 2 different ModbusTCP masters to connect to my PLC. I set up 2 ModbusTCP Slaves but I am getting an Error, "Both Slaves have been set to the same communication protocol."

They are set to different ports, and different Node ID's. Why am I getting this error?

Thanks,

Tim Snelling

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Hi Tim,

Unilogic doesn't support 2 slaves on the same protocol.

Since it's ethernet you may find that the two masters can connect and each poll the same slave without issue, this would depend on how rapidly the masters were each polling the slave.  This would definitely be a problem on RS485, but Ethernet can handle some level of simultaneous requests.  I suspect if both masters made a poll request at the same time, one of them would be buffered until the other one was answered, then the buffered request would be answered.

I understand if you want a more tightly engineered solution, and for that you would need to add something external like the Moxa Mgate product that can allow multiple masters to access a single slave.

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This sounds like a step backwards, as I've been doing this for about 10 years in VisiLogic on a V230 PLC's, and I've never had any issues. I switched to Unistream, to upgrade, I need this to work, it doesn't need to be 100% reliable, do i need to create a support ticket?

Thanks,

Tim

 

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11 hours ago, tim.snelling said:

This sounds like a step backwards

Agree.  Have never done this, but if you have and now can't on something way more capable, that's a bit silly.

Tim, if your other devices are Unitronics, would Unican work instead?

cheers, Aus

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Thanks AUS,

With the vision 230 PLC's, we are establishing a remote socket connection from 2 different applications that run on a windows OS workstation PC.

One application is connecting on the standard Modbus TCP port, and the other is connecting on a non-standard port. Both applications communicate with the PLC, and we have never had any issues with this. It's a simple setup for the 2nd socket connection via VisiLogic. So i'm confused with this issue showing up as an error in UniLogic...

We want to duplicate/improve the V230 program with a UniStream PLC.

If it was PLC to PLC, I assume UniCan would require CAN comm modules on each PLC?

Thanks, Tim

 

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I would definitely try a test setup with two ModbusTCP masters polling the single UniStream slave.  As I said it may just work exactly the way the V230 has been working.  If you don't have the actual masters, then test with a PC based emulator.

I took a quick look and see what you mean about setting up two Modbus configs and two Scan EX blocks in Visilogic. Easy to do.

If you used UniCAN you would need CAN modules on all PLCs.  But you say you are using a windows PC as the master, so I don't think CAN is the right option.

It's frustrating that a newer version doesn't do what the old one did.  If you want to push it further with Unitronics, then yes I would open a support ticket.

 

Hope this helps, Simon

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Thanks Guys, I appreciate everything.

My problem is, I can't test anything. Hardware is being assembled in control panels, at a vendor. and then shipping to the job-site. I have to go to the job-site, to connect up all of the external IO. And I'll be expected to have the logic close to completion by the time they put  power to the panels. The only good thing at this point, is one of the Masters is only for monitoring purposes, so if that one isn't working when the site goes live, it wouldn't be tragic. But I do need to resolve this soon. I went ahead and submitted a Support Ticket.

Thanks, Tim

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If you are interested, this is the reply that I received from my Support Ticket.

With the UniStream, you can have dozens of devices connect to the PLC on the same port. All you will need to do is set up 1 Modbus TCP slave instance, and point all of your devices to the same port (502).

So it appears I can delete my Slave on port 503, and all should be good, with dual connections (or more if needed) on port 502 :)

Tim

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17 hours ago, Ausman said:

Thanks Simon, I wasn't trying to clang your suggestion, just posing a possible alternative method. 

cheers, Aus

No worries, your post came before Tim posted about the masters both being PC-based.

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5 hours ago, tim.snelling said:

If you are interested, this is the reply that I received from my Support Ticket.

With the UniStream, you can have dozens of devices connect to the PLC on the same port. All you will need to do is set up 1 Modbus TCP slave instance, and point all of your devices to the same port (502).

So it appears I can delete my Slave on port 503, and all should be good, with dual connections (or more if needed) on port 502 :)

Tim

 

Hi Tim,

Good to have Unitronics confirm that.  I suspected it was the case but have never tried it.

Simon

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5 hours ago, tim.snelling said:

If you are interested, this is the reply that I received from my Support Ticket.

With the UniStream, you can have dozens of devices connect to the PLC on the same port. All you will need to do is set up 1 Modbus TCP slave instance, and point all of your devices to the same port (502).

So it appears I can delete my Slave on port 503, and all should be good, with dual connections (or more if needed) on port 502 :)

Tim

 

Hi Tim,

Good to have Unitronics confirm that.  I suspected it was the case but have never tried it.

Simon

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