Connect Arduino to PLC (Data Exchange)
@Paul, thanks for your suggestion. 

I want to go forward with TCP/IP. 
I have now setup a ESP8266 Modul. 
The ESP Modul is setup as a Server.
The Server on the ESP Modul is up and running. 
I'm also able to connect to the ESP-server with "Hercules", a Terminal Tool. 

All the example I found were establishing communicating with Browser and HTML. 
I have also checked this, but this is not what i want.

This is the current code communicationg with the web page to toggle a LED.

    void loop() {
    if (esp8266.available()) // check if the esp is sending a message
    {
    debug("available and waiting for command");
    if (esp8266.find("+IPD,"))
    {
      debug("Incomming Request");
      int connectionId = esp8266.parseInt();

      if (esp8266.findUntil("LED","\n")) digitalWrite(LED, !digitalRead(LED));

      String webpage = "&lt;h1&gt;Hello World!&lt;/h1&gt;Open [IP]/LED to Toggle LED on D9";

      if (sendCom("AT+CIPSEND=" + String(connectionId) + "," +          String(webpage.length()), "&gt;"))
      {
        sendCom(webpage,"SEND OK");
        sendCom("AT+CIPCLOSE=" + String(connectionId),"OK");
        debug("Send and Close");
      }
    }
  }
}


But the PLC has no web server. So now I would like to do the same thing as client through a terminal. 

How can i check what really had beed sent and what the ESP really received?
At this point sending the /LED command has no effect.

Terminal &amp; ESP



Thank you in advance for your advise