Best solution to read Modbus RTU with a compactlogix CPU

Hello

I need to design a panel to read (Maybe write also) some signals over modbus RTU protocol using an AllenBradley compact plc.

At first i was looking to use the serial port of a L32E thinking it would be like a ML1400 or a Siemens S7-1200 plc but..i'm screwed up it is RS-232 not 485...So i would need to add a 232/485 converter and reading here and there about the code, peoples seem to say it is complex to use etc...
Is it really complex ?

Since the L32E get pricey over time because it is phasing out, my other option is using a L30ER and a gateway but i still want something simple and cost effective....Prosoft modules tend to be expensives....Would it be a headhache to use another gateway brand if they don't have the right datafile to be implemented into the RS5000 program ? If so, i may spend the saving in time consuming and i would be better to stick with what works?

Any advices are welcome.

I would use a red lion datastation plus. they are inexpensive and pretty easy to setup compared to using a prosoft card.

What about anybus ??
http://anybus.com/products/gateway-index/anybus-communicator

Jeff23spl said:

I need to design a panel to read (Maybe write also) some signals over modbus RTU protocol using an AllenBradley compact plc.

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How many signals do you need to pass? Do you plan to increase the number of signals in the future?

Jeff23spl said:

At first i was looking to use the serial port of a L32E ... peoples seem to say it is complex to use etc... Is it really complex ?

Click to expand...

It depends on how skilled and knowledgeable is the programmer. For example, trying to write code for modbus communication without knowing nothing about serial communications can be a pain in the neck.

Anyway, download this manual Using Logix5000 Controllers as Masters or Slaves on Modbus and decide by yourself.

Jeff,

Real Time Automation offers gateway solutions for this. The 460ETCMM-N34-D is a very simple solution. Set up is web browser based and very simple. You will enter in your Modbus registers and CompactLogix tags that you will be reading and writing to. This gateway Auto Maps between the two. Support is always on top of any questions you have.

Matt

http://www.rtaautomation.com/product/460etcmm/

Prosoft make a nice module for CompactLogix

Rockwell makes (or at least used to make) a module that will let a CompactLogix controller operate as a Modbus RTU master. Its primary purpose is to communicate via DSI to PowerFlex drives but it also has Modbus RTU master settings. I’ve used it and it’s not too difficult to use.
https://www.scribd.com/doc/125276002/Modbus-Using-CompactLogix-1769-SM2

With a little bit of programming and a few euros (or dollars), you can do that with a Micro 820...
Ethernet port to talk to the L32E, Modbus RTU master, with built in functions...

Modbus is a protocol but the physical means by which it can be transferred are several.
232, 485, TCP

What device do you need to communicate with?
Port types available?

You could also put a MicroLogix 1100 (or 1400) in the system, have it read/write the Modbus RTU info and have the CompactLogix get the info from it.

diat150 said:

I would use a red lion datastation plus. they are inexpensive and pretty easy to setup compared to using a prosoft card.

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Usually the Datastation Plus is my hands down first choice with a Compactlogix. I've used Anybus and RTA's are decent too. I just like the Red Lion Crimson software and how easy the setup is. My choice would be:

1. Red Lion DSP
2. RTA
3. Anybus

If you don't mind "cheating", you can do this yourself easily (you can do it the right way easily too). Pretty sure there's a Rockwell KB with an example Modbus RTU master code. I have a Moxa RS485 adapter that I use with an L32E and I have precomputed message tables (not doing CRC calcs in the PLC) and simply check the response message length instead of the CRC, which basically checks for Modbus exceptions instead of message integrity. Admittedly this is bad practice, but basically you have a major problem somewhere else that you need to address if you start getting CRC errors. I only work with a few Modbus devices and know them inside and out. As long as they're wired correctly and the pre-transmit delay is correct for the combination of devices, I have near perfect communication.

Otherwise +1 for the Red Lion DSP. Prosoft module works fine but is too expensive. Really an insult by Rockwell that a MicroLogix has built-in Modbus support and Logix5000 class PLCs don't.

Also +1 to using a ML1100 or ML1400 since they're so cheap (cough www.fractioni.com)

HMS has a gateway which is integrated nicely with Studio5000, for more info see: http://www.anybus.com/products/gate...s/detail/ethernet-ip-to-serial-linking-device

//Patrick L

dginbuffalo said:

Usually the Datastation Plus is my hands down first choice with a Compactlogix. I've used Anybus and RTA's are decent too. I just like the Red Lion Crimson software and how easy the setup is. My choice would be:

1. Red Lion DSP
2. RTA
3. Anybus

Click to expand...

I'd use the Red Lion DSP! Cheap and easy!!!
I have used the ProSoft PLX31-EIP-MBS with good success. The price point is comparable to the DSP too