Unity Global Data vs. IO Scanning

Matt1234 · Jul 10, 2014

Hi,

I have an application with a Quantum PLC and an M340 PLC. The logic is regrettably to be split between the two and there will need to be a fair be of inter-PLC data exchange. Not having done much with inter-PLC comms on Schneider PLCs before, I'm interested in whether global data or IO scanning would be the preferred route here.

There will be a mix of data types. I can pack bit information into words if needed for more efficient transfer.

Opinions? Pros and cons of global data and IO scanning?

Thanks in advance.

robertkjonesjr · Jul 10, 2014

This is somewhat dependent on what products you choose - you indicate the platforms, but each of these platforms has multiple different network adapters/modules, with different features. As Schneider moves towards EtherNet/IP, their newer Ethernet modules support EIP and ModbusTCP, but I don't see Global Data anymore. I don't know what there plan is, but it's not a good sign for Global Data.

Global data is very easy to use but uses multicast w/UDP. Multicast data traffic usually has to be managed so requires extra work in configuration of your network and use of managed switches for GMRP. From memory, the Quantum will support either IGMP or GMRP, but M340 only supports GMRP on the NOE module. The NOC module, which is much newer, does not support global data.

IOScanner uses ModbusTCP and is easy to use, but requires managing located data a little closer, especially with the limit of number of registers that can be sent per configuration line.

Global data supports more data per packet so is more efficient, though with modern network speeds, this practically has no real benefit.

Global Data was always nice when I had multiple PLCs that all needed to see the same data. In this case, multicast makes sense as one packet is produced, and is then replicated by the network as needed (standard multicast behavior). In this case, it was worth the effort to manage the multicast traffic, but make sure your managed switches support GMRP if you use the M340.

IOScanner has it's benefits too. ModbusTCP is simple, and the setup for only two systems is not that hard. Since it uses TCP, really no network management is required, though managed switches are still recommended for the usual reasons.

Here are some other pros/cons.

And-Rey · Jul 10, 2014

If both of your PLC types are wired with Ethernet, I’d rather use IO scanning. It’s pretty easy to set it up (at least in my case) and we’ve never had issues with PLC communication through it.

Matt1234 · Jul 10, 2014

robertkjonesjr said:
This is somewhat dependent on what products you choose - you indicate the platforms, but each of these platforms has multiple different network adapters/modules, with different features. As Schneider moves towards EtherNet/IP, their newer Ethernet modules support EIP and ModbusTCP, but I don't see Global Data anymore. I don't know what there plan is, but it's not a good sign for Global Data.

Global data is very easy to use but uses multicast w/UDP. Multicast data traffic usually has to be managed so requires extra work in configuration of your network and use of managed switches for GMRP. From memory, the Quantum will support either IGMP or GMRP, but M340 only supports GMRP on the NOE module. The NOC module, which is much newer, does not support global data.

IOScanner uses ModbusTCP and is easy to use, but requires managing located data a little closer, especially with the limit of number of registers that can be sent per configuration line.

Global data supports more data per packet so is more efficient, though with modern network speeds, this practically has no real benefit.

Global Data was always nice when I had multiple PLCs that all needed to see the same data. In this case, multicast makes sense as one packet is produced, and is then replicated by the network as needed (standard multicast behavior). In this case, it was worth the effort to manage the multicast traffic, but make sure your managed switches support GMRP if you use the M340.

IOScanner has it's benefits too. ModbusTCP is simple, and the setup for only two systems is not that hard. Since it uses TCP, really no network management is required, though managed switches are still recommended for the usual reasons.

Here are some other pros/cons.

View attachment 32922

The quantum is using 140-NOE-771-01 cards. We're free to choose whatever we want for the M340.

It looks like there's a preference for I/O scanning looking at how the other PLCs on the site are setup.

robertkjonesjr · Jul 11, 2014

Matt1234 said:
The quantum is using 140-NOE-771-01 cards. We're free to choose whatever we want for the M340.

It looks like there's a preference for I/O scanning looking at how the other PLCs on the site are setup.

If they already do ModbusTCP with IOScanner, that's a reasonable reason to stick with that technology. Coupled with the uncertain future of Global Data, it's a good choice.

I would suggest the BMX NOC 0401 modules then for the M340 system as both the Quantum NOE and M340 NOC can be both ModbusTCP servers and clients at the same time and the NOC is currently being maintained.

Note that IOScanner is setup differently between the two products: the Quantum NOE uses the traditional Unity method, assuming you are using Unity for this, but the M340 (which requires Unity) will use a DTM to configure IOScanner. To act as a server, any unitID can be used with the Quantum NOE as a target, but for the NOC, be sure to use a unitID different than 255.

Unity Global Data vs. IO Scanning

Matt1234

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robertkjonesjr

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And-Rey

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Matt1234

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robertkjonesjr

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