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Old April 7th, 2021, 12:10 PM   #1
CQ21
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ML1100 as Modbus RTU Master

Hello all,

I am trying to setup my MicroLogix 1100 as a modbus RTU master for a modbus network containing multiple modbus RTU slaves. I currently have RSLogix500 (ver: 5.2) and want to know if this setup is possible with the software I have? If so, could anyone point me into the right direction on how to make this possible?

Also, my modbus slaves use the RS-485 electrical interface...how will this work? I heard the ML1100 has 3 channels: one ethernet, one RS-232, and I'm not sure what the last one is...If anyone could help, thanks in advance!
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Old April 7th, 2021, 02:23 PM   #2
Dravik
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The ML1100 Series B has a combo interface port (port 0), that supports either rs-232 or rs-485 signaling.

I have no idea about the version of software you have.

Start here for the instructions you need and then I would just check in the software directly.https://literature.rockwellautomatio...m001_-en-p.pdf
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Old April 7th, 2021, 03:50 PM   #3
CQ21
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Quote:
Originally Posted by Dravik View Post
The ML1100 Series B has a combo interface port (port 0), that supports either rs-232 or rs-485 signaling.

I have no idea about the version of software you have.

Start here for the instructions you need and then I would just check in the software directly.https://literature.rockwellautomatio...m001_-en-p.pdf
Thanks! Do you know how I can physically wire the master/slave modbus network for multiple slaves?
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Old April 7th, 2021, 04:00 PM   #4
Dravik
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With rs-485 signaling, it will depend if your devices are 2-wire(half duplex) or 4-wire(full duplex).

But basically you just tie your Data lines to each other (A to A, B to B) and terminate at the end w/ a typically 120ohm resistor.
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Old April 7th, 2021, 04:22 PM   #5
CQ21
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Quote:
Originally Posted by Dravik View Post
With rs-485 signaling, it will depend if your devices are 2-wire(half duplex) or 4-wire(full duplex).

But basically you just tie your Data lines to each other (A to A, B to B) and terminate at the end w/ a typically 120ohm resistor.
Thank you! It is a half duplex I believe. I was planning on using the 1763-NC01 cable and plug it into channel 0 and wiring my network from there. Would this work? The termination resistor goes across A to B correct?
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Old April 9th, 2021, 04:14 PM   #6
OkiePC
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Quote:
Originally Posted by CQ21 View Post
Thank you! It is a half duplex I believe. I was planning on using the 1763-NC01 cable and plug it into channel 0 and wiring my network from there. Would this work? The termination resistor goes across A to B correct?
The 1763-NC01 is right. It has a pin named TERM that allows you to add proper termination by connecting it to pin A.

You can get a slightly less expensive aftermarket 1763-NC01 from a forum member here. I have used his version and I like it better. You can actually read the text on the terminals in a dark panel much easier than the A/B version.

https://www.plccable.com/allen-bradl...in-micrologix/
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Old April 9th, 2021, 05:58 PM   #7
Ken Roach
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As always, RS485 vendors never quite do things the same way.

I think that you should be able to connect a MicroLogix 1100 to this Danfoss superheat controller using a 1763-PM01 cable.

The MicroLogix 1100's RS485 signal is not isolated from the rest of the logic. The "COMMON" terminal is the same as is used by the RS-232 port, and it should be connected to the DC Common of the controller's power supply as well.

The Danfoss EKD RS485 signal also looks like it's not isolated, and there is no Signal Common connection.

Because so many devices use the Shield of the cable as signal common, I would jumper COMMON to SHLD on the 1763-NC01 side.

The Data A and Data B signals might be correct to connect them "A-A" and "B-B". But with RS485 you never really know until you try.
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File Type: png EKD_to_1763NC01.png (63.9 KB, 18 views)
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Old April 9th, 2021, 06:03 PM   #8
Ken Roach
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I have a lot of good things to say about the CommFront product "HUB-485-4", which takes one RS485 or RS232 port input, and converts it to four isolated RS485 ports on the other side.

https://www.commfront.com/collection...ant=9077058115

I used this with a MicroLogix 1400 Series A controller a few months ago to connect its RS-232 port to four servo controllers that had themselves an RS485 port. This machine installation was notorious for noisy communication links, and the isolation on that device made it a non-issue. $150 to not have to worry about port isolation is cheap.

If I was doing this project I would probably use one of those and the SLC-5/05's Channel 0 serial port set up as a Modbus RTU Master.

But failing that, one of the browser-configured network gateways like the Spectrum Controls or RTA units would be my choice.
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