Which Allen-Bradley MicroLogix PLC models support Modbus

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It’s a common question that clients ask, “Which MicroLogix’s support Modbus?” In this article I’ll detail the answer.

MIcroLogix 1000 Crossed OutMicroLogix 1000

Today’s MicroLogix 1000 still has just one Mini-Din RS-232 “Channel 0” communication port limited to DF1 and DH-485. So for applications requiring Modbus you’ll need to look elsewhere, as the MicroLogix 1000 does not support Modbus.

MicroLogix 1200

MIcroLogix 1200 FrontSeries C versions of the MicroLogix 1200’s Mini-Din RS-232 “Channel 0” communications port supports DF1, DH-485, ASCII, MODBUS RTU SLAVE and MODBUS RTU MASTER. However, the series A and B models only support MODBUS RTU SLAVE.

Since “Channel 0” is limited to RS-232, to put the ML1200 on RS-485 I recommend the 1761-NET-AIC which is an isolated RS-232 to RS-485 interface converter. You’ll also want the 1761-CBL-HM02 cable to connect and power the AIC.

MicroLogix 1500MicroLogix 1500

Series C versions of the MicroLogix 1500’s Mini-Din RS-232 “Channel 0” communications port supports DF1, DH-485, ASCII , and MODBUS RTU SLAVE and MODBUS RTU MASTER. The LRP models also support DF1, DH-485, ASCII , MODBUS RTU SLAVE and MODBUS RTU MASTER on its DB9 RS-232 communications port labeled “Channel 1.” While series A versions of the LSP model has no MODBUS support, series B versions of the LSP and LRP do support MODBUS RTU SLAVE.

1761-NET-AIC Front View

Since “Channel 0” (and “Channel 1” on LRP models) is limited to RS-232, to put the ML1500 on RS-485 I recommend the 1761-NET-AIC. For “Channel 0″’s Mini-Din connection you’ll also want the 1761-CBL-HM02 cable to connect and power the AIC. For “Channel 1″’s DB9 connection you’ll need either a 1761-CBL-AC00 (17.7”) or 1747-CP3 (9.8′) (you’ll also need to provide 24vdc power to the AIC.)

MicroLogix 1100

MIcroLogix 1100All series of the MicroLogix 1100’s Mini-Din RS-232 “Channel 0” communications port support DF1, DH-485, ASCII, MODBUS RTU SLAVE and MODBUS RTU MASTER.

On the ML1100, Rockwell re-designed “Channel 0” removing the Mini-Din pins that previously provided 24vdc to accessories (like the AIC) and replaced them with RS-485 connections. So, to put the ML1100 on RS-485 you can use the Mini-Din to Terminal Block cable, the 1763-NC01.

MicroLogix 1400

MicroLogix 1400All series of the MicroLogix 1400’s Mini-Din RS-232 “Channel 0” and DB9 “Channel 2” communications port support DF1, DH-485, ASCII, MODBUS RTU SLAVE and MODBUS RTU MASTER.

Like the ML1100, the ML1400’s “Channel 0” port has RS-485 connections in place of the 24vdc power pins, so to put the ML1400’s “Channel 0” on RS-485 you would use the Mini-Din to Terminal Block cable, the 1763-NC01.

To connect the ML1400 DB9 RS-232 “Channel 2″ communications port to RS-485 I recommend the 1761-NET-AIC with a 1761-CBL-AC00 (17.7”) or 1747-CP3 (9.8′) (and don’t forget you’ll also need to provide 24vdc power to the AIC.)

1763-NC01
1763-NC01

Unique to the series B versions of the MicroLogix 1400 is the added support for MODBUS TCP on the “Channel 1” Ethernet port. The port is the standard RJ-45 style and supports 10 MBPS Half Duplex through 100 MBPS Full Duplex.

I hope the above information on which models of MicroLogix support Modbus was helpful. Later in the week I’ll cover which CompactLogix and ControlLogix models support Modbus. Until then, if you have any comments or questions please feel free to leave them by filling out the “leave a reply” form at the bottom of this page.

Sincerely,

Shawn Tierney
Automation Consultant
Insights In Automation

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Legacy Comments

  1. Shawn, great write up!! Very informative. Did you ever do one on “which ControlLogix or CompactLogix models support Modbus”, specifically Modbus RTU as master and slave? I’m really having a tough time selecting a model. I’d like to be able to have Modbus RTU slave to respond to a remote master non-AB PLC, and Modbus RTU master to talk to local non-AB drives.
    Thanks again!

    • Thanks William!

      I do have a draft of just that article, but I haven’t finished the research yet. However, here’s my notes so far:

      – For CompactLogix and ControlLogix processors with a “built-in” DB9 serial port, Rockwell includes with RSLogix 5000 sample code that allows you to communicate via MODBUS RTU using the serial port. The code works, but it’s a tad bit complicated, and I don’t know if a version exists for use with Rockwell’s Serial Port I/O Modules (so it can be used with new processors without serial ports.)

      – New CompactLogix processors (with USB ports, aka 5370) have updated internal Ethernet cards which support “open sockets,” and sample code (AOI) exists on Rockwell’s sample code website for Modbus TCP using the built in Ethernet port.

      – The old EWEB, and new EN2Tx/3TR also support open sockets, and in theory any L6 or L7 should be able to use the above sample code (AOI) for Modbus TCP, but I haven’t confirmed that.

      – Finally, Prosoft recently released some newer lower cost Modbus modules, so if all else fails that’s always an option.

      Well, those are all my notes! Would love to do all the fact checks and write it up as a blog but it will probably won’t be until February so hopefully these notes help some!

      Thanks again Will, and have a great New Year’s day 🙂

      Shawn Tierney

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  2. Great write up, but I think overall it’s far more cost effective to just replace my ML1200 with a $99 Koyo Click which doesn’t require any converters and directly takes rs485 cable. I wish all the big automation folks would realize we’re past the “Tower of Babel” days and there is no excuse for making something as univeral as Modbus as difficult and costly as possible.

    • Thanks for your comment Curt!

      I think many Automation folks in North American feel it worth the extra $100 to go with the MicroLogix over the Koyo because (1) they are familiar with it, and (2) it would honestly take more than $100 worth of time and effort to learn something new. And, that something new would now be the odd PLC out in their facility. I think this is also the reason why most haven’t used Rockwell’s $99 Click competitor, the Micro800.

      Thanks again for your comment!

      Shawn Tierney

      Did you find my comment helpful? Why not become a Premium Member with a small donation, and in return I'll give you a coupon for $10 of automation downloads! Find out more here

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