CODEWITHSUNDEEP
c#tcpclientplc
VeryIgnorantPerson
VeryIgnorantPerson

Reputation: 15

Sending CMD to PLC via TCP Client

I'm trying to send a command to a PLC that controls electronic lockers via a TCP Client. I am able to connect but it appears my command is not being read by the PLC.

I have the following code:

        private const string STX = "0x02";
        private const string ETX = "0x03";
        private const string STATUS = "0x30";
        private const string OPEN = "0x31";
        private const string SUM = STX + ETX;

        static void Main(string[] args)
        {
            var tcpClient = new TcpClient();
            tcpClient.Connect("192.168.1.190", 4000);

            if (tcpClient.Connected)
            {
                var networkStream = tcpClient.GetStream();
                if (networkStream.CanWrite)
                {
                    var ADDY = "00";
                    var asciiEncode = new ASCIIEncoding();
                    byte[] b = asciiEncode.GetBytes(STX + ADDY + OPEN + ETX + SUM);
                    networkStream.Write(b, 0, b.Length);
                    byte[] b1 = new byte[100];
                    var k = networkStream.Read(b1, 0, 100);
                    for (var i = 0; i < k; i++)
                    {
                        Console.WriteLine(Convert.ToChar(b1[i]));
                    }
                }
            }
        }

STATUS/OPEN are the commands that can be sent. The PLC came with some documentation and here is a picture of it. I assuming my CMD is wrong, how do I fix it? This is my first time trying to connect to and send/retrieve commands from a PLC. Any help is appreciated.

Upvotes: 0

Views: 1978

Answers (1)

stevenv
stevenv

Reputation: 431

You're on the right track, but the encoding of your command is wrong. Low-level protocols like these are tricky to get right.

Your byte array b contains the ASCII-encoded string "0x02000x310x030x020x03", encoded in ASCII, which translates to byte[22] { 48, 120, 48, 50, 48, 48, 48, 120, 51, 49, 48, 120, 48, 51, 48, 120, 48, 50, 48, 120, 48, 51 }while you want to be sending an array of the actual bytes 0x02, etc.

Try something like: byte[b] = new byte { 0x02, 0x00, 0x31, 0x30, 0x02, 0x03 }

See also http://www.december.com/html/spec/ascii.html to see how STX and ETX relate to the other ASCII characters (eg a-z, 0-9, etc).

Upvotes: 1

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