Q Use serial port to connect the GSM phone to send and receive short messages, how to program the implementation in the application?
Q We intend to develop a GPS system based on GSM short message mode, how to use SMS to communicate?
A First, we have to know what the SMS specification developed by Esti. The specification related to the short message transceiver we discussed mainly includes GSM 03.38, GSM 03.40 and GSM 07.05. The front two focused on the technical implementation of SMS (including encoding mode), which specifies the SMS DTE-DCE interface standard (AT command set). There are three ways to send and receive SMS information: Block Mode, Text Mode, and PDU Mode. Block Mode is already a former yellow flowers, and it is rarely used. Text Mode is a plain text method that can be used in different character sets, which can also be used to send Chinese short messages, but domestic mobile phones are basically not supported, mainly for Europe and America. PDU MODE is supported by all mobile phones, you can use any character set, which is also a default encoding method. Text Mode is relatively simple, and we don't discuss it without custom data transmission. The content described below is the implementation method of sending and receiving a short message under PDU MODE. The PDU string is a string ASCII code, consisting of '0' - '9', 'A' - 'f' These numbers and letters. They are 8-bit bytes of hexadecimal number, or the BCD code decimal. The PDU string not only contains the displayable message itself, but also contains many other information, such as the SMS service center number, the target number, the reply number, the encoding method, and the service time. Transmit and receive PDU strings, the structure is not identical. We first use two actual examples to explain the structure and arrangement of the PDU string.
Example 1 Send: SMSC number is 8613800250500, the other party number is 13851872468, the message content is "Hello!". PDU string from mobile phone can be 08 91 68 31 08 20 05 05 F0 11 00 0D 91 68 31 58 81 27 64 F8 00 00 00 06 C8 32 9B FD 0E 01 control specifications, specific analysis:
Segmentation Meaning Description 08SMSC address information Total 8 eight-bit bytes (including 91) 91SMSC address format (TON / NPI) with international format numbers (in front add ' ') 68 31 08 205 05 F0SMSC address 8613800250500, Supplement 'f' even 11 basic parameters (TP-MTI / VFP) send, TP-VP with relative format 00 message reference value (TP-MR) 00D target address number number total 13 decimal numbers (excluding 91 And 'F') 91 Target Address Format (TON / NPI) with International Format Number (Add ' ') 68 31 58 81 27 64 F8 Target Address (TP-DA) 8613851872468, 补 'f' even multiple numbers 00 Protocol Identification (TP-PID) is a normal GSM type, point-to-point mode 00 User information encoding mode (TP-DCS) 7-bit coding 00 validity period (TP-VP) 5 minutes 06 User information length (TP-UDL) actual Length 6 bytes C8 32 9B FD 0E 01 User Information (TP-UD) "Hello!"
Example 2 Receive: SMSC number is 8613800250500, the other party number is 13851872468, the message content is "Hello!". The PDU string received by the phone can be
08 91 68 31 08 205 05 F0 84 0D 91 68 31 58 81 27 64 F8 00 08 30 30 21 80 63 54 80 06 4F 60 59 7d 00 21
Control specifications, specific analysis:
Segmentation Meaning Description 08 The length of the address information is an eight-bit byte (including 91) 91SMSC address format (TON / NPI) with an international format number (in front add ' ') 68 31 08 205 05 F0SMSC address 8613800250500, supplement F 'makes even 84 basic parameters (TP-MTI / MMS / RP) reception, no more messages, there is a number of reply addresses 0D Reply Address number total 13 decimal numbers (excluding 91 and' f ') 91 reply Address Format (TON / NPI) with international format number (in front add ' ') 68 31 58 81 27 64 F8 Reply Address (TP-RA) 8613851872468, 补 'f' makes an even number 00 protocol identifier (TP-PID ) Is a normal GSM type, point-to-point mode 08 User information encoding mode (TP-DCS) UCS2 encoding 30 30 21 80 63 54 80 Time stamp (TP-SCTS) 2003-3-12 08:36:45 8 time zone 06 User Information Length (TP-UDL) actual length 6 byte 4f 60 59 7d 00 21 User Information (TP-UD) "Hello!" If the highest bit (TP-RP) of the basic parameter is 0, no reply address Three segments. Short messages issued from the Internet are often this situation. Note that the representation of the number and time is not compared to the normal order, and the odd number will be added to the odd number with 'F'.
Q The above two have appeared 7-bit and UCS2 encodings, please tell us about these coding methods.
A In PDU MODE, three coding methods can be used to encode the seminated content, which is 7-bit, 8-bit, and UCS2 encoding. 7-bit encoding is used to send a normal ASCII character, which encodes a string of 7-bit characters (highest bit 0) into 8-bit data, "compressed" into 7 per 8 characters; 8-bit The encoding is typically used to send data messages, such as pictures and ringtone, etc .; and UCS2 encodes to send Unicode characters. The maximum capacity of the user information (TP-UD) section of the PDU string is 140 bytes, so in these three coding modes, the maximum number of characters that can be sent is 160, 140, and 70, respectively. Here, all English letters, one Chinese character and a data byte are viewed as a character. It should be noted that the user information length (TP-UDL) of the PDU string is different in various coding methods. 7-bit encoding, refers to the number of characters of the original short message, not the number of bytes encoded. 8-bit encoding is the number of bytes. When UCS2 encodes, it is also the number of bytes, equal to twice the number of characters of the original short message. If there is a header (TP-UD) exists (TP-UDHI 1) in the TP-UD), in all encoding mode, the user information length (TP-UDL) is equal to the sum of the head length and the number of bytes encoded. If the compression algorithm suggested with GSM 03.42 (the TP-DCS is 3 bit is 001), the length is also the sum of the number of bytes or head length and the compression encoding after compression encoding.
The 7-bit encoding process will be described below with a specific example. We encode our English SMS "Hello!":
The source string is divided into a group (less than 8 in this example), compressed between the characters in the group, but there is no connection between each group.
The algorithm that implements 7-bit encoding and decoding with C as follows:
// 7-bit encoding
// psrc: Source string pointer
// PDST: Target Code String Pointer
// nsrclength: Source string length
// Return: Target Code String Length
INT GSMENCODE7BIT (Const Char * PSRC, Unsigned Char * PDST, INT NSRCLENGTH)
{
INT nsrc; // Source string count value
INT NDST; / / Target Code String Counting Value
INT nchar; // The number of characters in the group currently processed, the range is 0-7
Unsigned char nLEFT; / / Previous-byte residual data / / count value initialization
NSRC = 0;
NDST = 0;
// Distribute the source string into a group, compress into 7 bytes
// Cycle this processing process until the source string is processed
// If the group is less than 8 bytes, it can also be handled correctly.
While (NSRC { // Take the minimum 3 digits of the count value of the source string Nchar = NSRC & 7; / / Treat a source of each byte of the source string IF (nchar == 0) { / / The first byte in the group is only saved, and when you are processed NLEFT = * psrc; } Else { / / Other bytes in the group, add the right part to the residual data to get a target coding byte * PDST = (* psrc << (8-nchar)) | NLEFT; // Save the left part of the byte, saved as a residual data NLEFT = * psrc >> nchar; / / Modify the pointer and count value PDST of the target string; NDST ; } / / Modify the pointer and count value of the source string PSRC ; NSRC ; } / / Return to the length of the target string Return ndst; } // 7-bit decoding // psrc: source code string pointer // PDST: Target string pointer // nsrclength: Source Code String Length // Return: Target String Length INT GSMDECode7bit (Const unsigned char * psrc, char * pdst, int nsrclength) { INT nsrc; // Source string count value INT NDST; / / Target decoding string count value INT NBYTE; / / The number of bytes currently being processed, the range is 0-6 Unsigned char nLEFT; // Previous byte residual data / / Count value initialization NSRC = 0; NDST = 0; // Group byte serial number and residual data initialization NBYTE = 0; NLEFT = 0; // Divide the source data into a group, unzip into 8 bytes // Cycle the process, until the source data is processed // If you are less than 7 bytes, you can also process correctly While (NSRC { // Add the right part of the source by add to the residual data, remove the highest bit, get a target decoder byte * PDST = (* psrc << nbyte) | NLEFT) & 0x7f; // Save the left part of the byte, saved as a residual data NLEFT = * psrc >> (7-nbyte); / / Modify the pointer and count value of the target string PDST ; NDST ; // Modify byte count value NBYTE ; / / The last byte of a group IF (nbyte == 7) { // Additional target decoder bytes * PDST = NLEFT; / / Modify the pointer and count value of the target string PDST ; NDST ; // Group byte serial number and residual data initialization NBYTE = 0; NLEFT = 0; } / / Modify the pointer and count value of the source string PSRC ; NSRC ; } * PDST = 0; / / Return to the length of the target string Return ndst; } It should be pointed out that the 7-bit set of character sets is incomplete to the ANSI standard character set, and some printable characters are also arranged below 0x20, but the English letters, Arabic numbers, and common symbols are the same. Use the algorithm described above to send and receive pure English short messages, the general situation should be enough. If it is French, German, Spanish, etc., contain "å", "é" characters, then press the output to check the table above, see the provisions of GSM 03.38. 8-bit encoding actually does not specify what specific algorithm does not need to be introduced. UCS2 encoding is a 16-bit Unicode wide character that converts each character (1-2 bytes) according to ISO / IEC 10646. In the Windows system, especially in 2000 / XP, the API function can be simply invoked to implement coding and decoding. If there is no system support, for example, the mobile module is controlled by the microcontroller to send and receive short messages. In the Windows environment, the algorithms that implemented UCS2 encoding and decoding with C are as follows: // UCS2 encoding // psrc: Source string pointer // PDST: Target Code String Pointer // nsrclength: Source string length // Return: Target Code String Length INT GSMENCODEUCS2 (Const Char * PSRC, Unsigned Char * PDST, INT NSRCLENGTH) { Int ndstlength; // unicode wide character number Wchar wchar [128]; // unicode buffer // String -> Unicode string NDSTLENGTH = :: MultibyTetowideChar (CP_ACP, 0, PSRC, NSRCLENGTH, WCHAR, 128); // High and low bytes, output For (INT I = 0; i { // output a high byte * PDST = wchar [i] >> 8; // output low byte * PDST = Wchar [i] & 0xff; } / / Return to the length of the target coding string Return ndstlength * 2; } // UCS2 decoding // psrc: source code string pointer // PDST: Target string pointer // nsrclength: Source Code String Length // Return: Target String Length INT GSMDECodeucs2 (Const unsigned char * psrc, char * pdst, int nsrclength) { Int ndstlength; // unicode wide character number Wchar wchar [128]; // unicode buffer // High and low byte calls, meicode For (int i = 0; i { // Pre-high byte Wchar [i] = * psrc << 8; // Lower low byte Wchar [i] | = * psrc ; } // unicode string -> string NDSTLENGTH = :: widechartomultibyte (CP_ACP, 0, Wchar, NSRCLENGTH / 2, PDST, 160, NULL, NULL); // Output string adds an end conference PDST [NDSTLENGTH] = '/ 0'; / / Return to the target string length Return ndstlength; } With the above encoding and decoding modules, the short message string cannot be encoded as the format required by the PDU string, and cannot directly decode the user information in the PDU string as a short message string, because it is still a string and word The segment of the data between the data is converted. This transformation can be recirculated to call SSCANF and SPRINTF functions. The algorithms that do not need these functions are provided, and they also apply to single-chip, DSP programming environments. // Printing string to convert to byte data // such as "C8329BFD0E01" -> {0xc8, 0x32, 0x9b, 0xfd, 0x0e, 0x01} // psrc: Source string pointer // PDST: Target Data Pointer // nsrclength: Source string length // Return: Target Data Length INT GSMString2bytes (const char * psrc, unsigned char * pdst, int nsrclength) { For (int i = 0; i { / / Output high 4 digits IF (* psrc> = '0' && * psrc <= '9') { * PDST = (* psrc - '0') << 4; } Else { * PDST = (* psrc - 'a' 10) << 4; } PSRC ; // output low 4 digits IF (* psrc> = '0' && * psrc <= '9') { * PDST | = * PSRC - '0'; } Else { * PDST | = * PSRC - 'a' 10; } PSRC ; PDST ; } / / Return to the target data length ReturnNSRCLENGTH / 2; } // byte data transition to a printable string // {0xc8, 0x32, 0x9b, 0xfd, 0x0e, 0x01} -> "c8329bfd0e01" // psrc: source data pointer // PDST: Target string pointer // nsrclength: source data length // Return: Target String Length INT GSMBYTES2STRING (Const unsigned char * psrc, char * pdst, int nsrclength) { Const char Tab [] = "0123456789abcdef"; // 0x0-0xf character lookup table For (int i = 0; I { // output low 4 digits * PDST = Tab [* psrc >> 4]; / / Output high 4 digits * PDST = Tab [* psrc & 0x0f]; PSRC ; } // Output string adds an end conference * PDST = '/ 0'; / / Return to the target string length Return nsrclength * 2; } Regarding the compression algorithm in GSM 03.42, I haven't found it yet, here we don't discuss it. If you are interested, you can study it in depth. [Related resources] ◆ ETSI official website: http://www.etsi.org ◆ BHW98 column: http://www.9cbs.net/develop/author/netauthor/bhw98/
