How do I pull Modbus Data over Ethernet: CompactLogix

Without purchasing a prosoft card or similar, I would like to setup some message blocks to pull data from the ethernet port which is connected to a network switch that also has connected a Serial port server that takes RS232 serial modbus data and converts it to TCP Modbus data. The "server" is configured with a static IP and port of 502. Any examples or info would be appreciated.

CompactLogix Ethernet talks Ethernet/IP so unless there's some device that convert the Modbus data to E/IP, you are out of luck.

Something else seems weird in your description "connected to a network switch that also has connected a Serial port server that takes RS232 serial modbus data and converts it to TCP Modbus data". I very much doubt a network switch convert serial modbus to modbus TCP for you. Just because you carry modbus on ethernet through a serial/ethernt bridge doesn't mean it's been converted to Modbus TCP which is a different protocol than Modbus.

Assuming the modbus device talks serial modbus, I would try to talk through the serial port of the compactlogix which I believe does support modbus.

If you don't mind buying a couple of terminal servers (RS-232 / TCP/IP converters) you could use the CLX serial port and the sample code that A-B distributes with RSLogix5K to go RS-232 to TCP/IP and back again. The engineering costs will cost you more than a cheap PLC though...

Good Luck,

(8{)} .)

Everything has its cost. Prosoft cards and various gateways have a hardware cost, and implementing Modbus/TCP in ladder logic has a cost in memory and engineering time.

You can attempt it, if you have a new 5370-series CompactLogix that supports the Socket Interface feature.

The examples are in the RA Knowledgebase as Article ID 470365.

Ken Roach said:

Everything has its cost. Prosoft cards and various gateways have a hardware cost, and implementing Modbus/TCP in ladder logic has a cost in memory and engineering time.

You can attempt it, if you have a new 5370-series CompactLogix that supports the Socket Interface feature.

The examples are in the RA Knowledgebase as Article ID 470365.

Click to expand...

If we're talking HW costs I swear by that WAGO solution. The Modbus set-up is a total no-brainer whether for ethernet or serial, zero programming. The only programming that's needed is to move the data from the controllers EIP buffer to the Modbus read and write buffers. That shouldn't take more than 5 minutes. And the cost? Less, much less.

Cheers!

(8{)} .)
(Yosi)

harryting said:

Something else seems weird in your description "connected to a network switch that also has connected a Serial port server that takes RS232 serial modbus data and converts it to TCP Modbus data". I very much doubt a network switch convert serial modbus to modbus TCP for you. Just because you carry modbus on ethernet through a serial/ethernt bridge doesn't mean it's been converted to Modbus TCP which is a different protocol than Modbus.

Click to expand...

Harryting, just an FYI that there are several manufacturers out there that have this functionality. Ruggedcom definitely has it and I have investigated others over the last few years but none come to mind at the moment.

Also, if your Modbus is originating at a Scheneider PLC, make sure you look and see if they have any Ethernet/IP ethernet modules as Schneider supports Ethernet/IP natively.

Just to clarify, I have serial modbus data going into a Digi Terminal Server which has RS232 Input and TCP/IP ethernet output. I can configure it for Industrial Automation mode. which supports Modbus over IP. So looks like I will have to use a Prosoft card on the PLC side. The network switch is basically being used as a copper to fiber converter, and a convenient means to plug in a laptop for troubleshooting.

Details can be tricky with these sorts of things.

What is the exact model of Digi Terminal Server ?

Some devices support both "Modbus/TCP" and "Modbus over IP".

These are similar, but not identical, protocols.

My guess is that your device supports real Modbus/TCP, because you cited TCP Port 502. That's the standard TCP port for Modbus/TCP.

The module I would use on the CompactLogix side is the MVI69-MNET.

The serial Port server is a Digi PortServer TS4 MEI. And I believe the part number for the ProSoft card is the one I ordered.

If you have any of these processors AB has a ladder code that will "talk" modbus TCP right out of your ethernet port. You can grab the code from there website. If you go to the support center and search Modbus TCP the examples will come up.
1769-L16ER*
1769-L18ER*
1769-L18ERM*
1769-L23E-QB1
1769-L24ER-QB1B
1769-L24ER-QBFC1B
1769-L27ERM-QBFC1B
1769-L30ER
1769-L30ERM
1769-L33ER
1769-L33ERM
1769-L36ERM
1756-EN2T, EN2TR, EN2F, EN3TR modules firmware revision 5.007 or later **
1756-EWEB module, firmware revision 4.006 or later **