Logix 5000 Modbus TCP/IP

[DamianInRochester]

Damian,

The DSP and G3 are actually the same core, though they keep leap-frogging each other regarding the processor being used, memory fitted, etc. The new V2 G3s actually outperform the DSP at the moment, but that was a relatively recent change.

The DSP would have the same change in speed if you hit its web server while doing protocol conversion (and had a lot of tags on the screen), so if speed is critical, then you don't want to configure and use the virtual display in it either.

Speed will be dictated by the protocols chosen, and the amount of tags. The latter is probably obvious, but the former is very important. (We've seen protocols that will move 20 words in 10 seconds, and those that will move 10's of thousands in just over a second!)

If you have a specific application that you'd like us to benchmark, let us know - we'll see if we can simulate it here for you.

You can shoot the application information directly to Jeremy at [email protected] if you'd like. He does monitor the boards, but the back and forth questions and answers will be faster via email.

Thanks
Jesse

Jesse,
Thanks for great information. Although this application is already behind me, I may still take you up on your offer since it could impact future projects.
Our application was specifically EIP to ModbusTCPIP. All in all we were writing out about 16 bytes and reading in about 16 bytes of information. Or from a tag standpoint, 4 in and 4 out.
The data being passed was for "control" and so really did need to be pretty fast. Using the Modbus RTU connection we achieved about 80ms to 100ms full cycle updates. The best we achieved using the G3 as a gateway was about 200ms when the "least busy" screen was display. But then you could change the screen and all of the sudden be up around 1500ms. It is certainly possible we just didn't have something set optimally. We didn't have the luxury of time at that point to fiddle with it too much.

Thanks again,
Damian

 

[DamianInRochester]

The sample code that Control_Conn mentioned would work with the 1756-EWEB or the 1768-EWEB, but not with any of the CompactLogix integrated Ethernet controllers like the 1769-L32E or -L35E, or with the standard 1756-ENBT or 1756-EN2T modules.

In my opinion and experience, Modbus RTU and Modbus/TCP have not been made native protocols in the Logix family for two reasons: the relationship between RA and Prosoft Technology, and because of Group Schneider's past behavior with using patent litigation as a business tactic.

For the projects I work on, we're usually building Quantity 1, Serial Number 1 and the cost of engineering time to "roll our own" or even to evaluate another gateway type exceeds the price of an MVI-series module. Your mileage may vary.

Hi Ken,
Your point about the engineering investment is well received. There are circumstances with this particular arrangment that had the potential to be "the gift that keeps on giving" in the sense that it would have been a common architecture that would have been re-cycled. I also had the notion of possibly making it available to others for some small purchase price to help offset the development cost.
Based on the info you and others have given me it seems as though it would be a fool's errand. So I am glad I asked the question prior to just digging in.
I have found your point about group Schneider to be at least equally as applicable with AB as well. AB has never gone far out of their way to make it easy for third party products to be easily integrated into their architecture. Particulary when they have an offering that performs the same or similar function. That being said, from a business standpoint I can't blame them for being this way. It is all part of how they have been able to maintain their "top dog" status for such a long time.

 

[GeoffC]

Can't really see the legal side when Modbus and ModbusTCP are managed by the Modbus Organisation with Schneider only being 1 of a hundred or so members
An interesting development from Schneider are their new plc ethernet modules that support both ModbusTCP and EthernetIP on the same module, I'm in the process of using one in a project to integrate both types of devices on the one network.

 

[Ken Roach]

I'll be very interested to see how Schneider's dual-stack modules work out for you.

In the words of the fictional New York DA Jack McCoy: "I could indict a ham sandwich."

Just because a patent doesn't hold up in court doesn't mean that it can't be used to cause tens of millions of dollars in damage in the process. Group Schneider were the architects of the Solaia affair ten years ago, and RA has a very long institutional memory. That's just one of the reasons that you don't see Modbus/TCP in the ControlLogix family of controllers.

 

[NewToHSQ]

I know this is an old post but I hope someone is still watching it. The new Compact Logix L3 processors claim to have ModbusTCP support via Open Sockets. However, there are no programming examples for how to do it. I have 127 PLCs going in that need to communicate with some ModbusTCP equipment. I'd rather not spend $200k on third party modules to do it when the L3 should support it. Anyone done this that could share the basics of getting it working?

Thanks,

 

[Contr_Conn]

Modbus TCP application will be posted in a near future, but it only supports new dual port CompactLogix with open sockets functionality

Older controllers (L23E, l35E) don't support open sockets.

it will be also supported in ControlLogix EN2T platform

 

[NewToHSQ]

Can you define near future a little better? Since v20 supports it are we talking a few weeks or months?

 

[Ken Roach]

You can probably get it today from RA Technical Support; generally they have to do a little extra testing and documenting before something goes onto the Sample Code website.

I did a Modbus-like application with Open Sockets on the MicroLogix 1400 two weeks ago and it wasn't difficult. It helps if you're not doing a sophisticated application; mine had just two function codes.

There's a very nice Open Sockets technical bulletin for the ControlLogix family. EtherNet/IP Socket Interface Application Technique 1756-AT002

The first thing to keep in mind is that what you're doing is sending messages to the Socket object of the Ethernet module/subsystem. The Socket service is then doing the work of creating sockets, establishing TCP connections, and reading or writing data across them.

How many function codes do you need to implement ?

 

[NewToHSQ]

I am basically needing to interface to a MMI that only supports Modbus so I'm guessing the basic four functions to read values and set values. In the ML1400 rev B I can just check a box on the Communications dialog. I did see an example for the rev A processor but it was just serial modbus. Would you be willing to share what you did?

 

[Ken Roach]

So the MMI is going to be the Client, and the CompactLogix will be the Server ?

My application with MicroLogix 1400 was the other way around. I did it with Open Sockets because the vendor had implemented a custom Modbus function code.

 

[Contr_Conn]

I have no date, but from what I heard - week or two max.
Slave will be similar to the one that used to be in the knowledgebase since 2006.
Master is completely new and interface is very similar to the Modbus RTU for serial port.

Ken: No, you can't get it from techsupport today

 

[NewToHSQ]

I could do either as the MMI can be either. It does look like Rockwell is releasing an example in a couple weeks. I'd love to see what you did if your willing to share it. I often get into these issues where I need to do something "unique". I hate wiring stuff together when I don't have too.

 

[Ken Roach]

Let's go ahead and start a new thread, or send me a PM.

Most MMI devices don't have the ability to be Servers themselves; I'm curious about what this device is.

I happen to have a couple of 1769-L18ER's in the shop at this time, which also support the Open Sockets feature.

 

[NewToHSQ]

The device is by Unitronics and it's a hybrid MMI/PLC. We're going to use it as a backup pump controller and local display. The unit is 12" color for just over a grand.

 

[Contr_Conn]

I happen to have a couple of 1769-L18ER's in the shop at this time, which also support the Open Sockets feature.

You may not be able to do it with L1x:
master application for 4 connections takes about ~250K of memory.