https://forge.codesys.com/forge/talk/Engineering/thread/438e7c57cd/2025-05-16T14:31:02.493000ZRecent posts to Sequential read and triggering of Modbs RTU channels in application2025-05-16T14:31:02.493000Z2025-05-16T14:31:02.493000Zelsmarthttps://forge.codesys.com/u/elsmart/https://forge.codesys.com9d0dcbce15bc30115269647d2dc8928fcceef2ba

<div class="markdown_content"><p>Hello</p> <p>I need some help understanding how to use Modbus RTU (COM port) in Codesys enviroment. I defined a Modbus Server device (slave) in device tree and added some channels to read from (function 3). Also I set trigering mode to Application. I have a POU in which I want to trigger each channel one after the other something like this (C code for better visualisation):</p> <div class="codehilite"><pre><span></span><code><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="nc">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">channelsCount</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="err">{</span> <span class="w"> </span><span class="n">triggerChannel</span><span class="p">(</span><span class="n">channelsArray</span><span class="o">[</span><span class="n">i</span><span class="o">]</span><span class="p">);</span><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="k">Start</span><span class="w"> </span><span class="n">transmission</span> <span class="w"> </span><span class="k">while</span><span class="p">(</span><span class="n">channel</span><span class="p">.</span><span class="n">xBusy</span><span class="p">);</span><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="n">Wait</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">transmission</span><span class="w"> </span><span class="k">to</span><span class="w"> </span><span class="n">complete</span> <span class="err">}</span> </code></pre></div> <p>I have found ModbusChannel function block documentation but examples are scarce. I don't understand how rising edge triggering works. What would be the best solution for achieving sequntial channel triggering? What is the common way to read multiple Modbus channels once every time a specified POU is executed?</p></div>