title: Desktop SCADA Application - Reading and Writing to PLCs through C++
body: <p><strong>I did my best to search all topics regarding to SCADA and developing your own C++ desktop application to communicate with PLCs, but could not find any recent, or in my opinion, relevant topics that fit what I needed. If I missed them, a link to them would be very much appreciated. If I also happened to post this in the wrong section, or you can think of a better section for me to post this in, I will take it there.</strong></p>
  
  <p><strong>With that said, I thank you in advance for taking the time to read my questions, and appreciate any input you have to offer.</strong></p>
  
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  <p><strong>A little bit about what I'm doing</strong></p>
  
  <p>I'm currently in school for electromechanical engineering, and for my final year project I am developing a desktop application in C++ to monitor PLCs we have located within one of our labs.</p>
  
  <p>Within this lab, I have a pre-existing ethernet network connecting all PLCs to single point, which I am tying into with a PC, and will be doing all my work from there.</p>
  
  <p>I will be developing the application in Qt for an easy way to design the GUI, and giving me access to the QNetworkInterface as well as QTcpSocket.</p>
  
  <p>With that said, I wouldn't go as far as saying I'm an experienced programmer, but I have been fooling around with a few languages (i.e.: python, c++, c, php) for quite a few years, and am still learning, considering the learning NEVER stops.</p>
  
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  <p><strong>My questions</strong></p>
  
  <ol>
  <li><p>Is there any reference material I can read, that you can suggest, on the subject to more easily understand what sort of process I need to go through to receive information (i.e.: individual I/Os, status bits, tags, logs, etc...) from the PLCs directly, and not through an OPC server?</p></li>
  <li><p>If an OPC server is required, I've never dealt with OPC links other than using Rockwell Automations RSLinx to grab tags and display their values within excel (I had created a prototype using that exact method to start, but would like to move away from excel, and if possible, the OPC server (RSLinx) as well). What would you suggest to someone who knows nothing about the subject of OPC servers, or to my knowledge, OPC in general?</p></li>
  <li><p>Have any of you previously written your own application to do something similar, if not of the same nature to what I'm trying to accomplish?</p></li>
  <li><p>What advice or suggestions would you give for someone who is attempting this type of project?</p></li>
  </ol>
  
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  <p><strong>PS:</strong> As a start for this project, I would initially just want to get the reading of the I/Os (tags or addresses) to view what their current values are (closed or open for inputs, energized or not for outputs). But eventually I would also like to be able to write values to tags on the PLCs I'm monitoring based on the values I've received from them.</p>
  
  <p><strong>PSS:</strong> I would like to note again, that I am still a student, and am still learning about this subject in it's entirety. I would just like to ask for your patience, as I may not grasp things completely the first time!</p>
  
  <p><em>If I've missed any information you feel is pertinent to be able to provide an answer, please let me know! I will do my best to come up with said information in a timely manner!</em></p>
  
  <p>Thank you!</p>
  
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  <p><strong>EDIT #1</strong>: Added in another question, and altered my first question slightly</p>
  
  <p><strong>EDIT #2</strong>: Fixed up question 2</p>