https://forge.codesys.com/forge/talk/CODESYS-V2/thread/ca3bf2eca7/2020-02-27T23:03:51.549000ZRecent posts to Modbus TCP programming2020-02-27T23:03:51.549000Z2020-02-27T23:03:51.549000Zcincidudehttps://forge.codesys.com/u/cincidude/https://forge.codesys.com4fd74ca38464bc2c93e7d34075f5100b4672424e

<div class="markdown_content"><p>Hello,</p> <p>Actually I had the inputs mapped like:</p> <p>PLC_PRG.awModbusData<span>[1]</span>.0 := Input0; </p> <p>PLC_PRG.awModbusData<span>[1]</span>.1 := Input1; </p> <p>and it still did not work. Then somebody told me that "awModbusData" should be defined as a global variable. I did that and it worked like a charm. I would have never figured it out since the outputs mapped and worked correctly without declaring "awModbusData" as a global variable. Maybe you have a better idea.</p> <p>Anyways, my problem is solved for now. Thanks for your effort.</p> <p>Thanks,</p> <p>-Dude</p></div>

2020-02-27T23:03:49.931000Z2020-02-27T23:03:49.931000Zspfeifhttps://forge.codesys.com/u/spfeif/https://forge.codesys.com1e65a6950cda44f8459c4da2bd04cf87af11f00b

<div class="markdown_content"><p>Sounds like you did the following:</p> <p>Input0 := PLC_PRG.awModbusData<span>[1]</span>.0; </p> <p>Input1 := PLC_PRG.awModbusData<span>[1]</span>.1;</p> <p>This would cause the error you described change it to :</p> <p>PLC_PRG.awModbusData<span>[1]</span>.0 := Input0; </p> <p>PLC_PRG.awModbusData<span>[1]</span>.1 := Input1;</p> <p>Or you don't have awModbusData<span>[1]</span> configured as output instead as input this will not give it write access as well. Sounds like you might have one or both variables configured as inputs (readonly).</p> <p>The CoDeSys error will give you a line number in your code. Try to copy the code to make it easier to help.</p></div>

2020-02-27T23:03:48.329000Z2020-02-27T23:03:48.329000Zcincidudehttps://forge.codesys.com/u/cincidude/https://forge.codesys.coma5e5dc6b5b35698dadc8af23a850769b90e7f837

<div class="markdown_content"><p>As a follow-up to my own post, I was able to map the Outputs on my Festo PLC to the Mobbus TCP address space. This is the format I used:</p> <p>Output0 := PLC_PRG.awModbusData<span>[0]</span>.0;</p> <p>Output1 := PLC_PRG.awModbusData<span>[0]</span>.1;</p> <p>I can successfully switch on these outputs from my ModBus Client. However the same mapping does not work if I want to read in Inputs. Codesys gives the following error:</p> <p>Error 4020: Operands of 'ST', 'STN', 'S', 'R' must be variables with write access or direct address. </p> <p>I tried using direct addressing and symbolic names but does not work. Any ideas??</p> <p>Thanks,</p> <p>-Dude</p></div>

2020-02-27T23:03:43.791000Z2020-02-27T23:03:43.791000Zcincidudehttps://forge.codesys.com/u/cincidude/https://forge.codesys.coma3058be6a741b97c9fa120e84b1070a9bad8d869

<div class="markdown_content"><p>Hello,</p> <p>I'm a newbie to modbus communication. I have a Festo PLC and have configured the Modbus TCP server and can connect to it using a freeware Modbus TCP client </p> <p>Now I want to test the addressing. Apparently the addressing insde the Festo PLC is open and the user is free to choose his own addressing. I'm not sure if I have to write code in Codesys to map the IO and then address these addresses from the client? Or does Codesys provide a way to define this addressing?? Please advice or provide example if available.</p> <p>Thanks,</p> <p>-Dude</p></div>