Sending Unicode Messages (such as in Persian and Arabic) in C# using AT Commands through GSM Modem

Question

I am developing an application for GSM Modems (D-Link DWM-156) in C#.Net using AT commands. I have a problem sending Unicode messages (Such as messages written in Persian or Arabic). Here it is the core of my program:

SerialPort GSMPort = new SerialPort();

GSMPort.PortName = "COM6";
GSMPort.BaudRate = 9600;
GSMPort.Parity = Parity.None;
GSMPort.DataBits = 8;
GSMPort.StopBits = StopBits.One;
GSMPort.Handshake = HandShake.RequestToSend;
GSMPort.DtrEnable = true;
GSMPort.RtsEnable = true;

GSMPort.Open();

GSMPort.Write("AT\r");
Thread.Sleep(1000);
GSMPort.Write("AT+CMGF=1\r");
Thread.Sleep(1000);
GSMPort.Write("AT+CMGS=\"" + destinationNumber + "\"\r\n");
Thread.Sleep(1000);
GSMPort.Write(shortMessage+ "\x1A");

It works fine for English and ASCII letters. I have read this article and can send Unicode messages in Hyperterminal using AT commands:

AT [Enter]
OK
AT+CSCS="UCS2" or AT+CSCS="HEX" [Enter] ---> We have to convert our message to hex 
OK
AT+CMGF=1 [Enter]
OK
AT+CMGS="destinationNumber" [Enter]
> 0633064406270645002006450631062D06280627 ---> The hex format of our message (سلام مرحبا)
+CMGS: 139
OK

Since this commands worked correctly, I have added GSMPort.Write("AT+CSCS=\"UCS2\"\r"); to my application, and tried to send 0645 0631 062D 0628 0627 (مرحبا) or 0633 0644 0627 0645 (سلام).

GSMPort.Write("AT\r");
Thread.Sleep(1000);
GSMPort.Write("AT+CSCS=\"UCS2\"\r");
Thread.Sleep(1000);
GSMPort.Write("AT+CMGF=1\r");
Thread.Sleep(1000);
GSMPort.Write("AT+CMGS=\"" + destinationNumber + "\"\r\n");
Thread.Sleep(1000);
GSMPort.Write("0633064406270645" + "\x1A");

But unlike AT commands in Hyperterminal, destination does not receive correct letters. What is the difference between these AT commands in C# code and Hyperterminal code? I will appreciate if you help me to resolve this problem.

---

Additional information: As you know I have no problem for sending Unicode messages (such as Persian letters) by hyperterminal and using AT commands. In below code I try to send سلام, and "0633064406270645" is the hexadecimal form of it. But I receive □□□□ in my phone.

GSMPort.Encoding = UnicodeEncoding.GetEncoding(1256);
GSMPort.Write("AT\r");
Thread.Sleep(1000);
GSMPort.Write("AT+CSCS=\"UCS2\"\r");
Thread.Sleep(1000);
GSMPort.Write("AT+CMGF=1\r");
Thread.Sleep(1000);
GSMPort.Write("AT+CMGS=\"" + destinationNumber + "\"\r\n");
Thread.Sleep(1000);
GSMPort.Write("0633064406270645" + "\x1A");

In the hyperterminal environment, On the other hand, everything goes fine and I receive سلام.

AT [Enter]
OK
AT+CSCS="UCS2"
OK
AT+CMGF=1 [Enter]
OK
AT+CMGS="destinationNumber" [Enter]
> 0633064406270645 [Ctrl+Z]
+CMGS: 139
OK

I have noticed that in the hyperterminal properties if I check the "send line ends with line feeds" (it is in properties->Settings-> ASCII Setups, please check the picture below), I will have the same problem as I had in C# code. I think "send line ends with line feeds" is enabled in GSMPort.Write by default? If yes, how can I disable it?

Answer 1

I have finally found out how to resolve this problem. As I said in in the "Additional Information" section of my question, sending line ends with line feeds caused this mismatching between SerialPort in C# and AT commands in hyperterminal for sending Unicode messages. I have just replaced \r with \n line feeds. The modified code is as follow:

GSMPort.Write("AT\n");
Thread.Sleep(1000);
GSMPort.Write("AT+CSCS=\"UCS2\"\n");
Thread.Sleep(1000);
GSMPort.Write("AT+CMGF=1\n");
Thread.Sleep(1000);
GSMPort.Write("AT+CMGS=\"" + destinationNumber + "\"\n");
Thread.Sleep(1000);
GSMPort.Write("0633064406270645" + "\x1A"); 

Leave SerialPort.Encoding and SerialPort.NewLine properties unchanged. It is not necessary to change their default values, just set AT+CSCS="UCS2" to send messages in Unicode format.

Answer 2

First of all check your modem support unicode then change your code to this
we have to specify the correct DCS (Data Coding Scheme) for Unicode messages, which is 0x08.

We can set this value by changing the fourth parameter of the AT+CSMP command to '8':

AT+CSMP=1,167,0,8

    GSMPort.Write("AT\r");
    Thread.Sleep(1000);
    GSMPort.Write("AT+CSCS=\"UCS2\"\r");
    Thread.Sleep(1000);
    GSMPort.Write("AT+CMGF=1\r");
    Thread.Sleep(1000);
    GSMPort.Write("AT+CSMP=1,167,0,8\r"); //AT+CSMP=1,167,0,8
    Thread.Sleep(1000);
    GSMPort.WriteLine("AT+CMGS=\"" + destinationNumber + "\"\r\n");
    Thread.Sleep(1000);
    GSMPort.WriteLine("0633064406270645" + "\x1A");

Answer 3

The default encoding for SerialPort is Encoding.ASCII. Either set SerialPort.Encoding to an encoding to supports the character set you're using (like Encoding.UTF32) or use SerialPort.Write(char[], int, int) and convert your Unicode string to bytes in whatever way'd prefer.