I'm running a Modbus TCP server within node-red. I had a bit of an adventure forwarding the right ports from Docker , and now its signal is reachable from clients (sorry, I know it's master/slave config, but I'm more familiar with server/client analogies). The server log outputs the following: {"ty…

Solution: Turns out there was an error on my colleague's side, where his software was reading from addresses 4001, where it should have been reading from address 1 as they were already denoted as holding registers to begin with and didn't need the 400 preamble.

Basically, it's a Modbus TCP slave, and when masters query its holding registers (which the slave log says contain A) we get B. Here's the flows:

Slave (server) flows: [ { "id": "3decb5f518882686", "type": "subflow", "name": "live debug", "info": "", "category": "", "in": [ { "x": 240, "y": 160, "wires": [ { …

Master (client) flow: [ { "id": "64c7eb63152d8786", "type": "tab", "label": "localhost_ModBus_reserver_read", "disabled": false, "info": "", "env": [] }, { "id": "0b48912e93227892", "type": "inject", "z": "64c7eb631…

Update: My friend on the other end is now getting "real numbers", but they still seem to be out of range: [Brown&carroll client set 3 (1)] [Brown&carroll client set 3 (2)]

One is interpreting it as signed and the other as unsigned

:sweat_smile: both of those last were the output on my friend's end, he just switched views. My numbers are more along the lines of: [0,0,0,4,0,0,0,2560,0,0,0,38912,0,0,0,38912,0,0,0,0,null,null,null,0] i.e. register my number (broadcast) my number (received) his number (received, unsigned) h…

Is there any visible difference, e.g. is there some sort of bitwise operation that I don't know about that happens with Modbus signals?

I don't understand what you mean by your friends numbers and your numbers. Are you both accessing the same server in the same way?

Same server is being accessed (code above). I am accessing it via node-red installed on my machine (flow above in "Master"); my friend is using some proprietary software, but we're both getting different numbers to what is broadcast.

[image] Darren: Same server is being accessed (code above). Physically the same machine, or the same code on a different machine.

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Modbus TCP previews correct output, but receiving end gets garbage

General

Darren 15 May 2023 08:52 5

Update: My friend on the other end is now getting "real numbers", but they still seem to be out of range:

Topic		Replies	Views
ModBus TCP Read 32-bit registers Industrial	26	27019	26 January 2020
Node-red-contrib-modbus, problem with modbus serie General	24	656	6 December 2023
Questions about Modbus - UI controls and forwarding signals? General	18	478	23 June 2023
Modbus UINT16 to decimal? General modbus	35	974	2 October 2023
"Is Not A Valid Memory Write Message To Server" General modbus	9	530	17 May 2023

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Modbus TCP previews correct output, but receiving end gets garbage

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