Logix 5000 Modbus TCP/IP

Can anyone speak to the feasibility of developing a routine in a Control/Compact logix controller to implement Modbus TCP/IP?

Yes, I am aware and have used the Prosoft modules. I have used gateways. We've even used a RL Crimson HMI as a gateway although it was miserably slow.

What I am looking at is doing it with the Logix CPU itself.

I have used and modified the modbus RTU code to implement this serially.

Is their a fundamental deficiency in the Logix 5000 messaging capabilites that makes this essentially impossible to implement over ethernet?

The ordinary 1756-ENBT modules don't have the ability to generically open a socket and send data through it, like you can with just sending strings out the Channel 0 serial port.

In theory you could implement Modbus/TCP with a 1756-EWEB module, but I think it would be very difficult.

RA doesn't have a lot of reason to implement Modbus/TCP in the Logix platform, because of the strong relationship with Prosoft. Even with Schneider joining the ODVA and the release of a Modbus object in the CIP Specification a couple of years ago, I still haven't seen a CIP-based EtherNet/IP to Modbus bridge.

As of today you must use EWEB open sockets
Other modules don't have open socket functionality yet
EN2T platform will support open sockets in a near future with v20 release

There is a Modbus/TCP Slave code for EWEB available in KB since 2006. Can be uses AS-IS without any modifications
I am not aware of Modbus/TCP Master code but it can be easily done.

I'm not an expert like the other two guys who responded here... just I would like to point out the technote indicated in previous post:

Aid 33697

- [FONT=comic sans ms,sans-serif]fuzzy logic[/FONT]

Thanks Ken and CC for the info. I assume then that the Compact Logix will have the same limitations as the ENBT? Just so I understand, is this somehow a hardware issue (ie. the chip set they are using to drive the Ethernet, or is it more so software/firmware that AB just hasn't seen fit to bother adding?

Fuzzy, thanks for the tip. It looks as though I need a Techconnect contract to view it though.

you could do protocol conversion from using a digi one iap pretty cheap.

DamianInRochester said:

Can anyone speak to the feasibility of developing a routine in a Control/Compact logix controller to implement Modbus TCP/IP?

Yes, I am aware and have used the Prosoft modules. I have used gateways. We've even used a RL Crimson HMI as a gateway although it was miserably slow.

What I am looking at is doing it with the Logix CPU itself.

I have used and modified the modbus RTU code to implement this serially.

Is their a fundamental deficiency in the Logix 5000 messaging capabilites that makes this essentially impossible to implement over ethernet?

Click to expand...

I know you said you tried (something like) this but I have used the Redlion DSPLE in this type of application and I didn't find it to be slow at all.

Also, if you choose the option to have two Ethernet Cards in the DSPLE, you can even have two different networks if you need some kind of isolation.

JHarbin said:

I know you said you tried (something like) this but I have used the Redlion DSPLE in this type of application and I didn't find it to be slow at all.

Also, if you choose the option to have two Ethernet Cards in the DSPLE, you can even have two different networks if you need some kind of isolation.

Click to expand...

No, I used a G3 Red Lion HMI. It did work, but it was slow. The speed was also dependent on how much information was displayed on the screen. It was causing latency issues of more than 1 sec, which was way slower than I could tollerate.

Ironically, on that specific job I ended up switching over to Modbus RTU out of the L35E's comm port and was able to get reliable comms at a full update rate of about 100ms. It still bothers me that I had two devices on the same ethernet network and had to resort to an additional "serial" connection to get them to talk.

I am aware of many 3rd party gateways and prosoft module for this. I even have the prosoft module for this. I just wanted to explore the feasibility of doing it with the controller itself.

DamianInRochester said:

No, I used a G3 Red Lion HMI. It did work, but it was slow. The speed was also dependent on how much information was displayed on the screen. It was causing latency issues of more than 1 sec, which was way slower than I could tollerate.

Ironically, on that specific job I ended up switching over to Modbus RTU out of the L35E's comm port and was able to get reliable comms at a full update rate of about 100ms. It still bothers me that I had two devices on the same ethernet network and had to resort to an additional "serial" connection to get them to talk.

I am aware of many 3rd party gateways and prosoft module for this. I even have the prosoft module for this. I just wanted to explore the feasibility of doing it with the controller itself.

Click to expand...

I understand.

We just use a number of them to support various networks at our customer's sites. We have one application where one DSPLE is connected to two CompactLogix PLCs over Ethernet/IP and one Modbus/TCP controller and is serving data to a SCADA over Modbus/RTU (customer's existing network) and we haven't noticed any update issues.

We also use them on the controls side where a reasonable update rate is critical.

We have used it much more successfully the ProSoft devices.

Since I can't help you with the Modbus in the Controller itself, I'll back out.

JHarbin said:

We have used it much more successfully the ProSoft devices.

Click to expand...

Hi JH,
Can you explain more about the RedLion VS Prosoft? I have used the prosoft, but you seem to be implying that the RL has some advantages.

I wouldn't expect the G3 HMIs gateway functionality to compare to that of the dedicated unit. I think they view it as more of a "bonus" feature. On the G3 it would not be appropriate for control.

Thanks for the post.

DamianInRochester said:

Hi JH,
Can you explain more about the RedLion VS Prosoft? I have used the prosoft, but you seem to be implying that the RL has some advantages.

I wouldn't expect the G3 HMIs gateway functionality to compare to that of the dedicated unit. I think they view it as more of a "bonus" feature. On the G3 it would not be appropriate for control.

Thanks for the post.

Click to expand...

The DSPLE is not an HMI, it is a dedicated din-rail mounted Gateway Device. The things I appreciate about it are, reasonable cost, easy configuration, great technical support, and large driver selection. I did not find Prosoft to be as easy to configure or as versatile - just my opinion...

This is the device I am talking about - there are three versions and I have used all three, but the bare bones DSPLE is what we use the most. http://www.redlion.net/Products/HumanMachineInterface/DataStationPlus/DataStationPlus.html

We do not represent Redlion - we just use a fair number of them.

JHarbin said:

The DSPLE is not an HMI, it is a dedicated din-rail mounted Gateway Device. The things I appreciate about it are, reasonable cost, easy configuration, great technical support, and large driver selection. I did not find Prosoft to be as easy to configure or as versatile - just my opinion...

This is the device I am talking about - there are three versions and I have used all three, but the bare bones DSPLE is what we use the most. http://www.redlion.net/Products/HumanMachineInterface/DataStationPlus/DataStationPlus.html

We do not represent Redlion - we just use a fair number of them.

Click to expand...

Hi JH,
I think we are crossing signals. I do realize that the DSPLE is a dedicated gateway. I was merely stating that my experience with the G3 was not an apples to apples comparison since the DSP was designed for that very purpose and was just an afterthought on the G3. I have actually used DSP unit a long time ago myself but for a completely different application.

As far as DSPLE vs Prosoft, is your comment about the flexibilty related more to that fact that the RL can handle other protocols as well, or are there other things related just to EIP / Modbus/TCP translation that set it apart?

From what I remember, the DSP is much more cost effective than the Prosoft module, so if it also has performance advantages I am compelled to make a switch.

Thanks,
Damian

DamianInRochester said:

Hi JH,
I think we are crossing signals. I do realize that the DSPLE is a dedicated gateway. I was merely stating that my experience with the G3 was not an apples to apples comparison since the DSP was designed for that very purpose and was just an afterthought on the G3. I have actually used DSP unit a long time ago myself but for a completely different application.

As far as DSPLE vs Prosoft, is your comment about the flexibilty related more to that fact that the RL can handle other protocols as well, or are there other things related just to EIP / Modbus/TCP translation that set it apart?

From what I remember, the DSP is much more cost effective than the Prosoft module, so if it also has performance advantages I am compelled to make a switch.

Thanks,
Damian

Click to expand...

I just think it is easier "all around". Ask a question of Redlion - they monitor this regularly. They can give you performance info.

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

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.