Modbus Puns

I have a load cell amplifier that communicates over fieldbus and I am trying to read it via AD do-more h2 plc. It looks like it can communicate via Modbus, but is that the same? How do I go about finding the IP address of the amplifier? Am I completely off base? I apologize for my naivety, I am learning trial by fire here.

Hello,

I've recently been tasked with upgrading the motor controls on a pump station. We're adding a Toshiba AS3 VFD, replacing old single phase motor controls, start/run caps, run relay etc.

The intention is to have single phase in, 3-phase out (apparently this VFD will do this, and not the issue at hand).

Anyways, I've run into a problem with "extended" modbus registers/communications.

This Toshiba drive I'm hoping to install uses "extended" Modbus addresses and the RTU I was hoping to use (SCADApack32) only seems to talk standard range modbus for holding registers: 40001-49999**.** Has anyone had success using extended modbus in Telepace/Telepace Studio?

If not has anybody had success with a protocol converter/managed ethernet switch device that can convert from extended modbus to standard range, or from say Ethernet I/P (Common Industrial Protocol) to standard range modbus? I know Red Lion, Moxa, and Phoenix Contact make converters but I've never used them before.

Any help and recommendations appreciated.

I have to implement secure Modbus communication, i.e. Modbus over SSL, using the standard SSL library. Is there any primer / example / tutorial on that?

I'm trying to read data from an energy meter using Modbus (RS485). My RS485 connector has 3 pins the normal A & B and enable pin.

The problem I'm facing is that I am unable to read any data from the Holding Registers. I am using Arduino Framework. I'm unable to figure out if there is an issue with my ESP32 hardware or my program.

The modbus on the energy meter side is working as I'm able to read data using the following modpoll command: mbpoll -a 2 -r 157 -t 4:float -b 9600 -P none -o 1 -F1 /dev/ttyUSB0

All I need now is a library for ESP32 Modbus Client (Arduino Framework) and an example program. Also I need the logic to convert the data to Float as the device sends the data in encoded form in Big Endian and Little Endian.

I've tried using eModbus library but I could not get it to work (Probably coding mistake by me).

Thanks in Advance!

Most of the time if the documentation says a holding register 1072 holds my value and I read address 1072 I get a correct value. But sometimes when I read 1072 I don't get the correct value. So I go and check did I use the correct slave address, is my config correct etc, but in actuality all i had to do is deduct 1 from the address in the documentation to get the correct address that has my value. It happens rarely that deducting 1 from the address to get 1071 is always the last thing I remember to do after wasting my time.

Why is that some documentation specifies correct register address (the address that I send to the master) and some I have to deduct 1 from the address?

Hello,

I bought one of those Analog to Modbus modules where I can connect a bunch of 0-10V or 4-20ma sensors to the module and it will transmit that info over Modbus TCP/IP. All good so far. The data that is being transmitted is raw and needs to be scaled. Is there a way I can do this without a PLC and display it on computer/HMI?

Or do you think I need a PLC to just scale the information without having to use any of its IOs?

Thank you

https://www.reddit.com/r/SCADA/comments/r0ob5q/issue_with_sel_rtac_and_siemens_pac4200s_that_are/

I was told r/PLC was much more active, and I REALLY appreciate everyone who can help me with this issue. I didn't want to duplicate post between two threads, so I figured it'd be okay to link to this one :-)

Hello, I'm currently working on reading strings from a PLC to a Computer through it's modbus (ModbusTCP) registers.

The case is: I have 10 strings of 50 characters each one. And I convert each character to it's ASCII value and assign it to a register.

I mapped 50 registers in the modbus mapping, and iterate each string to overwrite the registers.

Should I just assign 500 registers and avoid the pain of iterations and overwriting the registers 10 times?

Application is not that big. And memory (From what I can visualize in the IDE) has no effect when assigning registers to a variable. What are your best practices when setting registers on the PLC?

Hi Reddit,

While working on Modbus devices I find myself often need to test a Server/Client with my PC but I cannot find a good (and free) simulator to do just that. So I made myself one: The YAMS.

It is still in early stage of development: a lot of functionalities are still to be implemented, but Modbus TCP Server/Client has its ReadInputRegister/ReadHoldingRegister/WriteMultipleRegisters working (in my test cases).

One key feature of YAMS is you can define the behavior and configuration of the simulated device with YAML file(s). This would, hopefully, make test automation much easier, and make it possible to build more close-to-real-life simulations.

Does it look like something you'd use? Anything you'd suggest correcting/adding?

Any feedback would be greatly appreciated!

Hello to everyone. I hope you are doing well.

I'm trying to establish a communication between my PC and my KINCO PLC. The manual states it supports MODBUS RTU protocol, so I downloaded two different Modbus Master simulator I found out: Multiway from OMRON and qModMaster. None of them seem to work properly. I attached some pictures of the messages I get.

https://ibb.co/f1mCSNt Multiway message

https://ibb.co/bP5cX1t qModMaster message

I include the configuration of the communication parameters.

https://ibb.co/nMty8D9 PLC parameters

https://ibb.co/6RTqVfC Multiway parameters

https://ibb.co/N1XTccd qModMaster parameters

According to the manual, in order to play the role of Modbus master with the PLC it's necessary to configure some instruction blocks (I'm programming in ladder). However, I could not find any block to configure as Modbus slave. I don't know what else I can do.

I'm in trouble with this task. Am I making some mistake?

Thanks for your attention.  Kind regards!

Hi!

Found a lot of useful information here on PLC programming. Had to ask one question about the Siemens software:

What’s the best practice on error handling with mb_client and modbus tcp?

I see that the block have a tendency to halt and not be able to restore coms if there are several disconnects. Changing connection ID restores coms instantly.

This made me think 🤔, is it a problem to run multiple client blocks on the same port (502). Thought Tia portal sorted this out automatically.

Also: tips on handling list coms and the data written to buffer DB. Do you set all array elements to zero in the code?

Hi All,

I'm currently doing a IBMS assignment at uni. My simple brain still cannot comprehend why BACnet or Modbus protocols is used or preferred on certain system. In a nutshell, I have to show topology on a system connecting to ICN backbone and suggest a protocol and give reason why I'm using that protocol.

If possible, can someone give a layman's explanation on how the two protocols work/differ or recommend me a good resource to go by?

Hi all, I’m about to start a project where I need to link 2 plcs with RS485, I’ve seen a few videos online about how to talk to modbus slaves and some about how to setup the plc as the slave but I really need both.

I want the user to press a button connected to either plc and turn lights on both of them at the same time.

Anyone done anything like this before?

I’m working with these things, with the intention of using them in a proprietary soft-plc (non-realtime).

Settinf and reading io is working. But there also are registers defining the attached modules, but it appears the docs are not quite right about the descriptive word you get back for some analog modules.

Anyone with similar experiences?

I have a machine that uses modbus tcp ip just for third party interaction with the machine I Can specify the ip and I have a spare port on a2 for my plc . My first attempt is using the Aoi add on instruction to communicate. My logic socket compatibility should be good. How do I go about finding all the comm setting for this instruction in relation to my machine? All they gave me from the company is a list of registers and addresses and whether or not they are read only or read and write.

Admittedly this is over my head but I’m pretty stubborn when I set out to do something lol and help or reading material would be appreciated? Thank you

i am looking for modbus master/slave library to be used with 8 bit & 32 bit controller. i have tried github but there so many options, couldnt really figure out

do you write your own modbus library or using any open source?

really appreciate all kind of help and assistance

I'm using Modbus RTU on the Micrologic 1400 to communicate with several motor controllers. When setting up my rung logic with MSG commands, can I send simultaneous MSG commands to each motor controller or do I need to sequence my logic so that only one MSG command is executing at time and step through each, one at a time?

Thanks

Okay so I am starting to get Into modbus for where I work. I have all the code to communicate over rs 485. I download it to the plc and that loads fine. But when I open modbus slave I can't seem to connect to the right thing. Do I need to get a USB to rs 485 connecter for my pc. Or can I do it over ethernet?