Lynn's Industrial Protocols over IP

Wednesday, January 03, 2007

Rockwell Bridging - Ethernet to DF1

Question: We have a MicroLogix 1500 with only 1 serial port. What Digi product can we use to enable Ethernet access from RSLinx or a HMI display?

The Digi One IAP allows bridging AB protocols:
- Ethernet/IP Master (such as ControlLogix) can query DF1 PLC
- CSPv4 Master (such as RSLinx, PLC5E or SLC5/05) can query DF1 PLC
- DF1 encapsulated in TCP/Ip (such as OPC server) can query serial DF1 PLC
- Modbus Master (TCP, RTU, or ASCII) can query DF1 PLC as-if a Modbus slave.

All of these can function concurrently, as the serial port is moving pure DF1.

The Digi One IAP cannot support DH485 because (like ProfiBus) the token rotation is too fast to be encapsulated over Ethernet successfully.

The general Rockwell Bridging is discussed in this PDF file:

Quick comparison of Digi One IAP to the 1761-NET-ENI:
ProductDigi One IAP1761-NET-ENI
Ethernet/IP to DF1 FullDuplexYESYES
CSPv4 (PLC5E protocol) to DF1 FullDuplexYESno
Modbus to DF1 FullDuplexYESno
DF1 encapsulated in TCP/IP or UDP/IPYESno
DF1 by port redirectionYESYES
Supports DF1 Radio ModemYES (next release "H")no
Maximum active Masters/Peers644
Configuration by WebYESno
Configuration by Telnet or SSHYESno

Basically, the Digi One IAP does everything the 1761-NET-ENI does (plus much more) except:
  • The Digi One IAP does NOT handle CIP encapsulated within DF1, which is required only for RSLinx to CompactLogix RS-232 port
  • The Digi One IAP does NOT have emails triggered by PLC MSG blocks
  • RSLinx won't talk Ethernet/IP through the Digi One IAP - it will talk "Ethernet Driver" fine. This is *NOT* related to existance of an EDS file. RSLinx talks via the 1761-NET-ENI because it is hard-coded to treat the ENI special. There is no EDS file information which RSLinx examines to function with the ENI.

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  • Lynn, I'm looking up for a quick way to implement DF1 over an Ethernet medium. I already have it working on Full Duplex for a serial(RS232) medium. The table that you presented here says that there is a way that only encapsulates DF1 on a TCP/IP packet. That works as simply as it sounds? I mean, open a TCP connection and start sending and receiving bytes and parsing them as was with DF1 over a serial medium? Tks!

    By Blogger A. Körbes, at 1:03 PM  

  • Yes, it is as easy as that. In fact, many OPC servers now support putting serial protocols like Modbus/RTU or DF1 into TCP encapsulation because it is very little extra work.

    The main things to remember:
    1) you'll want to build the message complete in memory, then send at one time - some serial tools write bytes one by one, that could cause timing problems over Ethernet.
    2) Rockwell/AB PLC do NOT understand DF1 in TCP, so you won't be able to talk directly with a PLC

    By Blogger Lynn August Linse, at 10:17 AM  

  • Tks for your reply. My main problem is that I need a way to talk (using Ethernet preferably TCP) directly to the AB PLC. As you said, DF1 directly on TCP won't work, what would you suggest? I've read briefly about some CIP messaging with specific commands that would allow me to use DF1 commands inside it. Tks in advance!

    By Blogger A. Körbes, at 12:20 PM  

  • At a bare minimum you'd need to do the following:
    1) issue the Ethernet/IP Register Session command
    2) issue CIP Unconnected Sends, which 'route' through the backplane to the Logix processor
    3) The Unconnected Send moves an Exec_PCCC command, which is like the DF1 but starts at 0x0F cmd only (no SRC or DST)

    I wrote a white-paper once which outlined the bare minimum to do this. I'll see if I can find.

    By Blogger Lynn August Linse, at 2:51 PM  

  • Okay, I added a new blog entry today pointing to my old white-paper.

    By Blogger Lynn August Linse, at 3:06 PM  

  • Lynn, you mention "the Digi One IAP does NOT handle CIP encapsulated within DF1, which is required only for RSLinx to CompactLogix RS-232 port."

    Does this mean OPC Topic configuration in RSLnx is not possible? I have DigiOne IAP bridging CompactLogix DF1 to Ethernet/IP and require OPC server for RSView 32 stations. I am trying to replace existing 1756-NET-ENI.

    Thanks for any suggestions!

    By Blogger Robin, at 8:10 PM  

  • Actually, OPC (assuming you mean a third party-tool) is a VERY different animal from RSLinx.

    You don't say if your OPC driver is Ethernet/IP or DF1.

    If Ethernet/IP, and if you configure it to move SLC5 typed read/writes, then the DOIAP works fine.

    If DF1 Full-Duplex (which the NET-ENI doesn't handle), then many OPC servers allow you to place pure DF1 Full Duplex into a TCP/IP socket (or UDP).

    If you create a DF1 serial destination on the DOIAP, then you can connect to TCP port 2101 (or 2101 for 2nd port) with raw/pure DF1 Full-Duplex and the multi-master works fine. This config is 'magic' and you cannot disable it. Literally, the DOIAP code sees your DF1-FD from TCP port 2101 as a virtual 3rd or 4th serial port with a DF1-FD master on.

    Then the DF1 is querying the PCCC Logix 'files' created by RSLogix 5000 directly. You can't access tagged data like this.

    By Blogger Lynn August Linse, at 8:17 AM  

  • Oh, by the NET-ENI "not handling DF1" - I meant it can't handle DF1 encapsulated in TCP or UDP.

    Of course the NET-ENI supports serial DF1 on the RS-232 port.

    By Blogger Lynn August Linse, at 8:18 AM  

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