https://forge.codesys.com/forge/talk/CODESYS-V2/thread/e4b047d577/2025-03-18T10:17:47.451000ZRecent posts to Modbus TCP client reconnection problem2025-03-18T10:17:47.451000Z2025-03-18T10:17:47.451000Zfmonhttps://forge.codesys.com/u/fmon/https://forge.codesys.com5172973c7454de1768ef026b6bfd0c26d3ce73df

<div class="markdown_content"><p>Problem solved</p> <p>The client modbus cycle time was linked to a task at 500ms. Whereas the channel modbus was at 200ms. Certainly problem of packages synchronisation.</p> <p>I let the client modbus cycle time to be handled by itself (See attachement) --&gt; "Use the bus cyle time parameters" (traduce from french)<br/> See attachement</p></div>

2025-03-17T08:52:51.295000Z2025-03-17T08:52:51.295000Zfmonhttps://forge.codesys.com/u/fmon/https://forge.codesys.comc27bc43371785528f998e99e2d79df8f97014b27

<div class="markdown_content"><p>Hello,</p> <p>I am using codesys Modbus TCP client (4.4.0.0) to communicate with a python modbus server (package pyModbusTCP). </p> <p>I first start my python server on the distant machine.<br/> After a fresh codesys compilation, a plc connection/transfer and a PLC run, the modbus connection is OK. Every time in this context the connection is created correctly.</p> <p>When I shut down the server, the modbus connection falls, that is normal.<br/> When I restart the python server, impossible to recreate the modbus connexion. With the client autoreconnection, I see on my server that the client tries to connect but unsuccesfully. I have the following message :</p> <blockquote> <p>DEBUG:pyModbusTCP.server:accept new connection from ClientInfo(address='192.168.1.20', port=33476)<br/> DEBUG:pyModbusTCP.server:Exception during request handling: NetworkError('recv return null')</p> </blockquote> <p>I tried to stop the codesys client and to restart it with these commands :</p> <div class="codehilite"><pre><span></span><code><span class="nv">Modbus_TCP_Client</span><span class="o">.</span><span class="nv">xStop</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nv">True</span><span class="p">;</span><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="nv">Or</span><span class="w"> </span><span class="nv">False</span> <span class="nv">Modbus_TCP_Client</span><span class="o">.</span><span class="nv">Enable</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nv">True</span><span class="p">;</span><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="nv">Or</span><span class="w"> </span><span class="nv">False</span> <span class="nv">Modbus_TCP_Server</span><span class="o">.</span><span class="nv">Enable</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nv">True</span><span class="p">;</span><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="nv">Or</span><span class="w"> </span><span class="nv">False</span> </code></pre></div> <p>I tried to confirm the error manually to force reconnection with:</p> <div class="codehilite"><pre><span></span><code><span class="nv">Modbus_TCP_Server_Motors</span><span class="o">.</span><span class="nv">xConfirmError</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nv">TRUE</span><span class="p">;</span> </code></pre></div> <p>I tried also this command to STOP/RESET/START client and server (codesys side) but nothing happens :</p> <div class="codehilite"><pre><span></span><code><span class="nv">status_client</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nv">Modbus_TCP_Client</span><span class="o">.</span><span class="nf">SetCommunicationState</span><span class="p">(</span><span class="nv">eRequestedState</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nv">DED</span><span class="o">.</span><span class="nv">DEVICE_TRANSITION_STATE</span><span class="o">.</span><span class="nv">STOP</span><span class="p">);</span><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="o">.</span><span class="nv">RESET</span><span class="w"> </span>&amp;<span class="w"> </span><span class="o">.</span><span class="nv">START</span> </code></pre></div> <p>The answer of this function when executed is "status_client = NOT_SUPPORTED". Is it normal ?</p> <p>It seems that is a socket problem, but I do not understand if it is on the client or server side.<br/> I tried a modbus simulator called "ananas.exe" and the result is the same. Impossible to get a modbus client reconnection.</p> <p>What is different at the first client connection and at a reconnection attempt ?</p> <p>Thanks for your help</p></div>