send English SMS with GSM Modems (D-Link DWM-156)

问题:

I am developing an application for GSM Modems (D-Link DWM-156) in C#.Net using AT commands. I have a problem sending English SMS. I try to send "hello", But I receive □□□□ in my phone or ...exept hello.

serialPort1.DataBits = 8;
serialPort1.Parity = Parity.None;
serialPort1.StopBits = StopBits.One;
serialPort1.BaudRate = 9600;

serialPort1.DtrEnable = true;
serialPort1.RtsEnable = true;
serialPort1.DiscardInBuffer();
serialPort1.DiscardOutBuffer();


serialPort1.WriteLine("AT\r");
Thread.Sleep(2000);

serialPort1.WriteLine("AT+CMGF=1\r");
Thread.Sleep(1000);

serialPort1.WriteLine("AT+CMGS=\"09390149196\"\r")
Thread.Sleep(2000);

serialPort1.WriteLine("hello" + "\x1A");
Thread.Sleep(1000);

回答1:

Few fixes (maybe more but I don't see full-code).

• Do not use WriteLine() but Write() because for \r (alone) is the command line and result code terminator character.
• SerialPort.WriteLine() by default writes a usASCII encoded string but your GSM modem expect strings encoded as specified with an AT command. Set SerialPort.Encoding property to a specific encoding and send CSCS command. You can ask supported encodings with CSCS=? AT command. Even if default GSM should apply I'd avoid to rely implicitly on this.
• You do not need to wait after each command but you have to wait for modem answer (checking for OK or ERROR strings).

From docs:

A command line is made up of three elements: the prefix, the body, and the termination character. The command line prefix consists of the characters "AT" or "at" [...] The termination character may be selected by a user option (parameter S3), the default being CR.

In pseudo-code:

void SendCommand(string command) {
    serialPort.Write(command + "\r");

    // Do not put here an arbitrary wait, check modem's response
    // Reading from serial port (use timeout).
    CheckResponse();
}

serialPort.DataBits = 8;
serialPort.Parity = Parity.None;
serialPort.StopBits = StopBits.One;
serialPort.BaudRate = 9600;
serialPort.DtrEnable = true;
serialPort.RtsEnable = true;
serialPort.Encoding = Encoding.GetEncoding("iso-8859-1");

serialPort.DiscardInBuffer();
serialPort.DiscardOutBuffer();

SendCommand("AT"); // "Ping"
SendCommand("AT+CMGF=1"); // Message format
SendCommand("AT+CSCS=\"PCCP437\""); // Character set

SendCommand("AT+CMGS=\"123456\"") // Phone number
SendCommand("hello" + "\x1A"); // Message

To check response (absolutely avoid arbitrary waits!) you can start with something like this (raw untested adaption so you may need some debugging, see also this post):

AutoResetEvent _receive;

string ReadResponse(int timeout)
{
    string response = string.Empty;

    while (true)
    {
        if (_receive.WaitOne(timeout, false))
        {
            response += _port.ReadExisting();
        }
        else
        {
            if (response.Length > 0)
                throw new InvalidOperationException("Incomplete response.");
            else
                throw new InvalidOperationException("No response.");
        }

        // Pretty raw implementation, I'm not even sure it covers
        // all cases, a better parsing would be appreciated here.
        // Also note I am assuming verbose V1 output with both \r and \n.
        if (response.EndsWith("\r\nOK\r\n"))
            break;

        if (response.EndsWith("\r\n> "))
            break;

        if (response.EndsWith("\r\nERROR\r\n"))
            break;
    }

    return response;
}

Adding _receive.Reset() just before you send your command and of course also adding OnPortDataReceived as handler for SerialPort.DataReceived event:

void OnPortDataReceived(object sender,
    SerialDataReceivedEventArgs e)
{
    if (e.EventType == SerialData.Chars)
        _receive.Set();
}

If you have some trouble (but you can connect) you may replace \r with \n. Some modems incorrectly (assuming <CR> has not been mapped to anything else than 13 using S3 parameter) use this character as command line terminator by default (even if it should be present in output only for V1 verbose output). Either change your code or send appropriate S3.