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Old April 2nd, 2021, 03:03 PM   #1
CQ21
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Modbus over RS-485 for SLC 5/05

Hello all!

I am currently trying to read some temp values from a M2B+ controller (link: https://www.diecastmachinery.com/Use...e%20Manual.pdf) which uses modbus RTU protocol. I wish to monitor the temp values from the controller into my SLC 5/05 that has OS series C FRN 13 (Processor FRN 6) using RS-485 electrical interface (that's what the temp controller uses).

I am aware that I may need an RS-232 to RS-485 converter but I'm not sure what that model/PN # is. Additionally, I am using RSLogix500 (Ver: 5.2) and would like to know if its possible to do this with the software I have? If so how can I configure my channels and program to make this work? I am fairly new/unfamiliar to all of this and I hope there may be someone that can help me out!

Thanks!

Last edited by CQ21; April 2nd, 2021 at 03:50 PM. Reason: more accurate description
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Old April 6th, 2021, 12:25 PM   #2
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Quote:
Originally Posted by CQ21 View Post
Hello all!

I am currently trying to read some temp values from a M2B+ controller (link: https://www.diecastmachinery.com/Use...e%20Manual.pdf) which uses modbus RTU protocol. I wish to monitor the temp values from the controller into my SLC 5/05 that has OS series C FRN 13 (Processor FRN 6) using RS-485 electrical interface (that's what the temp controller uses).

I am aware that I may need an RS-232 to RS-485 converter but I'm not sure what that model/PN # is. Additionally, I am using RSLogix500 (Ver: 5.2) and would like to know if its possible to do this with the software I have? If so how can I configure my channels and program to make this work? I am fairly new/unfamiliar to all of this and I hope there may be someone that can help me out!

Thanks!
Page 45 of the manual shows the options on the M2B+ you need to communicate RS232 Modbus RTU.

The SLC500 port 0 is RS232 already.

If you RS232 on both sides, you need to hack together a serial cable - in the past, 9 pin to 9 pin, both sides - https://www.se.com/ww/en/faqs/FA241117/

Then you can refer to another thread - http://plctalk.net/qanda/showthread.php?t=118548

That goes through the firmware requirements. I think your SLC500 software may be too old.

I can't find anything that mentions how to configure the Modbus Master protocol on the SLC500 side. That must be in the SLC 500 documentation.

I don't have the SLC hardware - I think that's about all I can do to help
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Old April 6th, 2021, 02:26 PM   #3
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Your software is too old. Must be version 8.1 or higher. When you have the correct software, you can go to channel config and configure Channel-0 as RTU Master.
Your CPU firmware is fine, Modbus support began at 11, you are at 13.
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Last edited by Ken Moore; April 6th, 2021 at 02:38 PM.
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Old April 7th, 2021, 09:06 AM   #4
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Your software is too old. Must be version 8.1 or higher. When you have the correct software, you can go to channel config and configure Channel-0 as RTU Master.
Your CPU firmware is fine, Modbus support began at 11, you are at 13.
Thank you! Will this work for a Modbus RTU network of multiple slaves? Is there any documentation on the configuation of the ports in RSLogix500? Do you happen to know how I can convert from RS-485 to RS-232 also?

Much appreciated!
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Old April 7th, 2021, 10:48 AM   #5
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When you set up the SLC channel for Modbus Master, you will write MSG instructions and pick Modbus function codes as the choice for what type of message. Then the MSG dialog box will offer a place to enter the target SLC address for the data, the Modbus address from the slave, and the slave Modbus ID, so all the protocol info is there for a multi-drop network built into the SLC code. We use this a lot with radio modems where there are multiple end points, but the master SLC connects via RS-232 to the main radio modem.

A long time ago, I worked on a system that used a panel din rail mounted rugged RS232 to RS485 converter that was famous for handling industrial protocols nicely. I don't recall the make/model, but I will let others with more current experiences chime in.
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Old April 7th, 2021, 03:40 PM   #6
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When you set up the SLC channel for Modbus Master, you will write MSG instructions and pick Modbus function codes as the choice for what type of message. Then the MSG dialog box will offer a place to enter the target SLC address for the data, the Modbus address from the slave, and the slave Modbus ID, so all the protocol info is there for a multi-drop network built into the SLC code. We use this a lot with radio modems where there are multiple end points, but the master SLC connects via RS-232 to the main radio modem.

A long time ago, I worked on a system that used a panel din rail mounted rugged RS232 to RS485 converter that was famous for handling industrial protocols nicely. I don't recall the make/model, but I will let others with more current experiences chime in.
Thanks! Do you happen to know how to wire the multiple slave Modbus network? Since there is only 1 RS-232 channel how will I add more slaves? This is all very new to me so sorry if it's a dumb question...
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Old April 7th, 2021, 05:29 PM   #7
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This is for different system, but the wiring section should be similar to what you need. Don't forget the terminating resistors.
https://www.coolswitch.at/Files/10/2...th%20of%20600m.

For multidrop, you will need a RS232 to RS485 adapter. Like OkiePC, it has been awhile since I used one, and cannot recommend a vendor/model.
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Last edited by Ken Moore; April 7th, 2021 at 05:32 PM.
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Old April 7th, 2021, 06:51 PM   #8
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This will allow you to connect to the SLC5/05 via either Ethernet or DF1 (full duplex) and to the M2B+ via MB RTU RS485 (it must be a MB RTU slave). You also won't have to create any message instructions (the Gateway handles all of the communications). It's also very easy to setup using a web browser.


https://www.spectrumcontrols.com/pro...ersal-gateway/
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Old April 9th, 2021, 09:20 AM   #9
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This will allow you to connect to the SLC5/05 via either Ethernet or DF1 (full duplex) and to the M2B+ via MB RTU RS485 (it must be a MB RTU slave). You also won't have to create any message instructions (the Gateway handles all of the communications). It's also very easy to setup using a web browser.


https://www.spectrumcontrols.com/pro...ersal-gateway/
Thank you very much this all seems good! So I can just plug in my RS-485 devices and use the tag map to copy/create the tags in my SLC 5/05? However, there is one slight issue...you see I have my SLC 5/05 already on LAN via its ethernet port. How can I use this while also keeping my SLC 5/05 on my LAN??
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Old April 9th, 2021, 10:29 AM   #10
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SLC5/05 via either Ethernet or DF1
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Old April 9th, 2021, 04:18 PM   #11
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Quote:
Originally Posted by CQ21 View Post
Thank you very much this all seems good! So I can just plug in my RS-485 devices and use the tag map to copy/create the tags in my SLC 5/05? However, there is one slight issue...you see I have my SLC 5/05 already on LAN via its ethernet port. How can I use this while also keeping my SLC 5/05 on my LAN??
You would just need to configure the gateway for the SLC and have them both on the same ethernet network. I have not used the Spectrum controls device, but have worked on systems with similar hardware. It is definitely simpler than adding a RS232 to RS485 converter and writing PLC code to perform the messaging. The Gateway speaks multiple languages including the Ethernet protocol needed by the SLC.
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Old April 9th, 2021, 04:20 PM   #12
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How many temperature controllers do you need to connect to ?

What's your budget ?

Do you plan to update your RSLogix 500 software so you can program MSG instructions for Modbus in the modern firmware ?

For ease of use and Web-based configuration, the Spectrum Controls and Real Time Automation gateways are probably the most straightforward. Both are good value for money, especially if you're a Modbus or SLC-500 MSG programming novice and don't want to spend a lot of time on software.
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Old April 9th, 2021, 04:42 PM   #13
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Originally Posted by OkiePC View Post
You would just need to configure the gateway for the SLC and have them both on the same ethernet network. I have not used the Spectrum controls device, but have worked on systems with similar hardware. It is definitely simpler than adding a RS232 to RS485 converter and writing PLC code to perform the messaging. The Gateway speaks multiple languages including the Ethernet protocol needed by the SLC.
Thanks! It seems much easier! I've looked into it and I've seen a few examples between micrologix modbus to SLC/PLC EIP. But do you think it would work for my temp controllers as they don't really have a "tag" defined, just a register address?
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Old April 9th, 2021, 04:58 PM   #14
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How many temperature controllers do you need to connect to ?

What's your budget ?

Do you plan to update your RSLogix 500 software so you can program MSG instructions for Modbus in the modern firmware ?

For ease of use and Web-based configuration, the Spectrum Controls and Real Time Automation gateways are probably the most straightforward. Both are good value for money, especially if you're a Modbus or SLC-500 MSG programming novice and don't want to spend a lot of time on software.
So far I have 2 temp controllers that I wish to put on my modbus network, but there will be more in the future I'm sure. As far as my budget goes...I'd say maybe around $2K, would like to keep it on the cheaper side of things but if you have a solution that's a bit more, that will work, I'd be open to it.

I have already planned to upgrade my RSLogix500 software regardless but I am not the best programmer...I would lean more towards the spectrum controls or RTA gateways. Do you know what RTA gateway models might be best for my application?
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Old April 9th, 2021, 05:00 PM   #15
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Thanks! It seems much easier! I've looked into it and I've seen a few examples between micrologix modbus to SLC/PLC EIP. But do you think it would work for my temp controllers as they don't really have a "tag" defined, just a register address?
Yes, Modbus is all function codes and Modbus addresses. There are no tags in Modbus. I think tags first appeared in PLCs a year later in 1980
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