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E14 Community recommendation for ModBus TCP client

colporteur — Thu, 11 Jun 2026 21:20:08 GMT

I am looking for an application to query a ModBus TCP interface on a scale head?

The company I am working for has recently installed a RiceLake 1280 scale indicator with a Modbus TCP interface. The scale indicator is IP capable and resides in a network DMZ. The goal is to have a cloud vendor pull scale data over the network from the Modbus interface. I'm looking for an application that can query the Modbus interface to confirm communication with the interface.

The scale vendor recommended an application in order to set the Modbus TCP interface IP address. I managed to get that working, proving the interface IP answers an IP ping. DMZ rules have been set in place to isolate the indicator. I want to test that the cloud vendor can get to the Modbus interface and pull the data. I'm thinking maybe there is a software tool like minicom is for serial communication, except the tool is for Modbus.

E14 has some great Modbus resources but nothing to match my search. A Modbus client query tool. I'm hoping there is a community member that has experience with Modbus TCP and that they could recommend application software to perform the task.

RE: E14 Community recommendation for ModBus TCP client

colporteur — Wed, 24 Jun 2026 21:58:36 GMT

I will close this post by first saying thank you for your input. Sounding out the problem and getting suggestions was helpful in arriving at the solution.

I culled a link for oceancontrol windows GUI client from the link beacon_dave provided. shabaz python client established a connection, I just didn't invest in generating a query. It did confirm it was working. BigG input reminded me of net cat a network test tool I had used many moon ago. I confess net cat was the one I used the most.

Since I was only looking to confirm a connection through the firewall, net cats ease of use made it ideal for quick testing. Supported on windows and linux was bonus. I had to learn the syntax for Windows:( It is not the same as linux.

With a confirmed modbus tcp interface available it is off to configure and test a VPN end to end solution that will connect the company and vendor. Thanks again for you input.

RE: E14 Community recommendation for ModBus TCP client

BigG — Sat, 20 Jun 2026 19:34:55 GMT

Ah fantastic. Not that I would know (noob here). Apparently with netcat, you can transmit the structured Modbus application bytes and see if the hardware replies. This completely validates both the firewall rules and the device's availability in one go.

Searching online brought up this page: stackoverflow.com/.../send-modbus-rtu-request-via-tcp-with-netcat-and-catch-the-response

RE: E14 Community recommendation for ModBus TCP client

colporteur — Sat, 20 Jun 2026 14:39:13 GMT

I completely forgot about CLI netcat! I recall you can setup a transmit and receiving end on ports you are examining.

Man I miss tech coffee breaks. All those minds in one place was a great technical pool of knowledge.

RE: E14 Community recommendation for ModBus TCP client

shabaz — Fri, 19 Jun 2026 16:03:20 GMT

I cannot take the credit, AI wrote that code, I merely pointed it at the 1280 user manual, and it spit out Python code, I merely ran it and told it of any errors, so it could correct it. The screenshot below shows what I asked it originally. It's not perfect as you noticed, since it could have provided more helpful output or automatically abort a test rather than hang.

Regarding the TCP connection etc., I'm very familiar with that part only because I ended up developing some products that heavily relied on network features/functions, I believe I would struggle with a lot of it if I had to learn it on my own.

RE: E14 Community recommendation for ModBus TCP client

colporteur — Fri, 19 Jun 2026 15:35:13 GMT

I'm humbled by your knowledge and thankful that you are willing to share.

Many eons ago, when my skins had less wrinkles, I recall training with a senior aviation electronics technician in a course. He took the the time to share his experience. The stuff I learned in that short interaction I have never forgot.

I can't comprehend how you extracted the information from the manual that enabled you to write code and decode the output for the modbus tcp interface. I'm envious.

I recall listening to a lecturer speaking Russian. I figured if I listened hard enough I would understand Russian. Never understood a word! I have combed the manual and reviewed your code thinking if I try hard enough I will gain the knowledge. It is not working.

If I was forty years younger, I would invest the time. I accomplished the goal. Just have the test the firewall rules set and be done. Thanks again.

I tried you trick of connecting to an IP that didn't support modbus tcp and noted the error. I suspected your code was working. Great work on a first attempt.

RE: E14 Community recommendation for ModBus TCP client

colporteur — Fri, 19 Jun 2026 15:22:20 GMT

I believe the video is where I found the bread crumbs to the site.

RE: E14 Community recommendation for ModBus TCP client

shabaz — Thu, 18 Jun 2026 15:49:31 GMT

Here is how the 1280 did in fact respond during the first test case:

Your log file indicates the 1280 returned a status code 269 which in hex would be 0x010d or 0000 0001 0000 1101 in binary.

According to the user guide, that means:

No error,
tare not entered,
center of zero,
weight OK,
standstill, primary units, tare not acquired, gross weight,
first channel (I don't know if that means channel 0 or channel 1).

Anyway, perhaps this is now too much detail, since it's already clear the TCP connection to the 1280 did successfully, and that's all you requested. However, the test case shows that the actual Modbus TCP protocol layer is successfully being received and sent by the 1280 (from experience/being burnt with various protocols, I wanted the simulation to include Modbus TCP; there are plenty of situations where a TCP connect alone is simply insufficient to be sure that the next layer will pass).

RE: E14 Community recommendation for ModBus TCP client

beacon_dave — Thu, 18 Jun 2026 15:23:01 GMT

FYI that Ocean Controls tool was one of the ones demonstrated in the video link I posted previously.

https://youtu.be/RiYHcFqbxCo?t=1946

RE: E14 Community recommendation for ModBus TCP client

shabaz — Thu, 18 Jun 2026 15:22:05 GMT

Hi Sean,

Your output is successful. Here is what you'd see if there was no TCP connection at all:

And this is what would be seen if the TCP connect occurred, but there was no response data from the 1280 end; it would just hang on Step 1 of the first test case (which has three steps):

However in your client_output file, I see this, so it got past step 1 (and 2 and 3) and all of the first test case was successful.

Your log file stops on the second test case step 1. I'm guessing you've got the real 1280 device attached, and it simply doesn't like the second test case (which is fine, since the test cases were written based on the ambiguous user guide, so the second test case happens to attempt a register that the real 1280 doesn't like. The log file shows that second test case was using a read register # 40257, that's the only difference from the first test case. So, since it's now confirmed your real 1280 doesn't use 40257, that could be deleted from the list inside the cloud_app_simulator.py file if you wished. But it's already confirmed that the 1280 end did respond with TCP data during the first test case.

RE: E14 Community recommendation for ModBus TCP client

colporteur — Thu, 18 Jun 2026 15:17:07 GMT

An update on the goal of finding a modbus TCP client.

My attempt with Shabaz offering wasn't successful so I moved onto hits from a google search for modbus tcp client.

oceancontrols has such a beast for Windows. https://oceancontrols.com.au/software-modbusview-tcp-ocs-011.html The free software timeout every 15 minutes. Once restarted you have to setup communication. I installed the software in a Windows sandbox to test.

I believe it is important to provide a return on investment. Your responses are valuable here is a return.

I don't know Modbus protocol and I am not in the market to learn it. My goal was to find software that I could use to test the ability to connect to a modbus tcp interface through the firewall to the DMZ.

The oceancontrol software is easy to install from their download.

The Configure tab (Ellipse A) is where you set the IP address of the device you want to connect to. There is no ability to save this in the free software therefore every 15minutes you have to start over.

Pressing the Start Polling button generates Status window messages and the poll window changes to Active.

Under the Communication tab you bring up a log or monitor window. The top half of the monitor window transmit screen, shows polling numbers and the bottom half polling response numbers (Ellipse B) poll 36 gives a return of poll 36. There is a polling number receive for every transmit.

A quick cmd window netstat -an shows a connection established (Ellipse C) to the IP address and port of the interface. When polling is stopped this connection disappears. YES! We are connecting and communicating to the modbus tcp interface.

I was unsuccessful when I tried using the registers to write and read. It would be nice to interact, request a read of the scale head and see some data but that is not necessary to reach my goal. I have little programming knowledge so I abandoned that exercise.

For this test the modbus tcp interface was outside the DMZ. Next step is to reposition the interface inside and start testing communication into the DMZ.

RE: E14 Community recommendation for ModBus TCP client

colporteur — Thu, 18 Jun 2026 13:49:47 GMT

I've used your client side program. It appears to connect but generates errors.community.element14.com/.../client_5F00_output.zip

RE: E14 Community recommendation for ModBus TCP client

BigG — Sat, 13 Jun 2026 16:57:32 GMT

A slight deviation/distraction but I wondered if the page you shared would make for a Github project (something I'm exploring at present). So, I opened up the question to Gemini...

The file you linked is an excellent core element of a project because it has:

Defined Terminology: It explicitly details domain-specific terms (like coils, discrete inputs, holding registers) so a developer doesn't have to guess.
Clear Structures and Mappings: It provides precise payload formats (<additional_address> <modbus_request_pdu> ...) and error/exception tables.
Actionable Utility: A developer trying to write a Modbus communication driver in Python, C, or Go can look directly at this markdown file and know exactly how to structure their bytes.

An ideal GitHub project is simply a centralized workspace that solves a specific technical problem or serves a clear purpose for its target audience. It can be pure code, pure documentation, or a mixture of both.

RE: E14 Community recommendation for ModBus TCP client

shabaz — Sat, 13 Jun 2026 14:23:03 GMT

I'm doing a similar thing.. I'm getting AI to help me with my notes, since the Wikipedia pages (and other resources) have info scattered, and I just wanted it condensed. This is a work-in-progress, I still need to check, and will test with my real device, and capture some traffic and so on: modbus_tools/modbus_rtu_format.md at main · shabaz123/modbus_tools (but please don't use this yet, since I'm still learning!).

In some ways sometimes it's better coming at things from a beginner perspective when writing notes, because then one learns what's unclear in existing online documentation, and those are the areas I like to focus on, because it's almost guaranteed I will eventually forget again and so I will want to re-read quickly.

I got AI to write me the software for the checksum (CRC) that RTU uses (TCP doesn't require it), verified it on Windows with real examples, and will also build it on a Pi Pico to double-check (there's no endianness issue, but I still want to test on at least one microcontroller).

RE: E14 Community recommendation for ModBus TCP client

BigG — Sat, 13 Jun 2026 14:07:13 GMT

Having never done this, I was curious. So, decided to ask my AI assistant as this is how I am now learning these days. You learn by doing. The benefit with this method is that it pays to be wrong and AI is great at doing that. It simply sets a direction and off you go. Maybe this is helpful...

gemini.google.com/.../9aba1ba75b87

RE: E14 Community recommendation for ModBus TCP client

shabaz — Sat, 13 Jun 2026 13:47:30 GMT

Hi! Might depend on what the cloud app vendor can do. Depending on what they're using (e.g. PaaS) they might not have as much flexibility to confirm if things are working at that low level (i.e. TCP socket). Hence to preempt that, if the test included a higher level (i.e. valid Modbus TCP messages) then that may be quicker for them to be confident the comms is working fine, even though the Modbus TCP messages can be garbage (valid garbage). If the cloud app vendor can work at a low-level in the stack then you're right, just a TCP level check might be sufficient.

RE: E14 Community recommendation for ModBus TCP client

shabaz — Sat, 13 Jun 2026 13:32:29 GMT

Here's a video of the Python code in case it's needed to see how to run it..

https://youtu.be/1O3W2kOLMrQ

RE: E14 Community recommendation for ModBus TCP client

colporteur — Sat, 13 Jun 2026 13:21:05 GMT

I don't see the need at the moment to rabbit hole wireshark. If I can query the interface (i.e. a client tools) and get results, I'm out of here. TCP passes the DMZ rules I'm golden. Myopic focus, can connection pass packet pass the FW.

RE: E14 Community recommendation for ModBus TCP client

colporteur — Sat, 13 Jun 2026 13:17:50 GMT

Yeah I got excited with this find. I've considered a cut and paste to see if I can get a phthon scrpt to work. Shabaz has given me a better starting point, so I will start there first if an app search is unfruitful.

RE: E14 Community recommendation for ModBus TCP client

shabaz — Sat, 13 Jun 2026 13:03:10 GMT

WireShark is awesome.. just noticed there's an extension that will do Modbus-RTU too: jzhvymetal/WiresharkSerialAdapter: Wireshark Serial Adapter for Windows

I'm currently writing up some notes for myself regarding RTU, (will put them on GitHub) but will probably test with WireShark to confirm I've interpreted things right.

RE: E14 Community recommendation for ModBus TCP client

beacon_dave — Sat, 13 Jun 2026 11:03:44 GMT

[quote userid="123345" url="~/technologies/industrial-automation-space/f/forum/57027/e14-community-recommendation-for-modbus-tcp-client/236099"]I suppose one other thing worth doing is perhaps running WireShark, and examining if it successfully decodes whatever is sent by these two simulators. I didn't try that (I've not got WireShark installed currently)[/quote]

Learn the Modbus RTU and Modbus TCP protocol in 1 hour:
Tools for testing Modbus (Modbus TCP View, Wireshark)

https://www.youtube.com/watch?v=RiYHcFqbxCo&t=2006s

RE: E14 Community recommendation for ModBus TCP client

beacon_dave — Sat, 13 Jun 2026 09:54:52 GMT

[quote userid="37381" url="~/technologies/industrial-automation-space/f/forum/57027/e14-community-recommendation-for-modbus-tcp-client/236101"]I figured someone here would have used a modbus client. Coming up zeros.[/quote]

"...This also required using Modbus (TCP) within a Python script to be able to send commands..."

https://community.element14.com/challenges-projects/project14/musictime/b/blog/posts/100-year-old-player-piano-gets-an-update-music-time-via-python-and-modbus-tcp

RE: E14 Community recommendation for ModBus TCP client

colporteur — Sat, 13 Jun 2026 01:15:53 GMT

Thanks S. I will it a try next week.

I have a programmer friend that did something simulator. He had a python script running a modbus server. I couldn't buy him enough beer to make a client:(

I figured someone here would have used a modbus client. Coming up zeros.

RE: E14 Community recommendation for ModBus TCP client

shabaz — Fri, 12 Jun 2026 21:34:27 GMT

Hi Sean,

While it's not the best protocol for this (it's a bit "naked"! and the cloud app vendor ought to have come up with better proposals to be honest), but anyway, I was interested, because by coincidence I'm just getting going with Modbus RTU currently (RS-485 instead of TCP, some differences in the protocol). I got curious enough to try to find the user manual for the 1280 Modbus TCP card. I gave that to AI, and it generated the Python code attached below. It complained that the user manual was vague in places, which it is, so I told it to try to make a simulator that accepted a few different function codes, and then try to simulate the cloud side too).

The screenshot shows the 1280_simulator.py file running at the left side, it just sits and waits for a connection.

On the right window, you can see the cloud_app_simulator.py file running, it makes a TCP connection to the 1280 simulator, and then tries a few function codes.

Currently the code transmits to port 127.0.0.1 and port 1502, you'd need to modify both of those to suit your needs.

Please don't ask me for modifications or tweaks, I don't know Modbus TCP nor what the AI did! : ) It might be ok but it might not. It might completely fail.

I suppose one other thing worth doing is perhaps running WireShark, and examining if it successfully decodes whatever is sent by these two simulators. I didn't try that (I've not got WireShark installed currently). I only tried running the Python code on Windows, it should work with Linux but I can't be sure.

community.element14.com/.../modbus_5F00_tcp_5F00_python.zip

RE: E14 Community recommendation for ModBus TCP client

obones — Fri, 12 Jun 2026 20:17:44 GMT

Well, telnet will tell you if the connection can be established, which is a first "layer" of tests.

After that, a quick search for modbus TCP lead me to this reddit with a few suggestions: https://www.reddit.com/r/PLC/comments/ncp724/modbus_tcp_computer_client/?show=original