SMS sending

  The SMS sending format is: AA 02 +11Bytes mobile phone number + data. It should be noted that the length of the data does not exceed 140Byte, and in order for the mobile phone to display correctly, it needs to be encoded by UNICODE, so each frame has a maximum of 70 characters. The mobile phone number is encoded in ASCII. For example, the ASCII code of "1" is 31, and the ASCII code of 13595313404 is 31 33 35 39 35 33 31 33 34 30 34.
  Take sending "Hello" to the mobile phone 13595313404 as an example, the UNICODE code is: 4F60 (you) 597D (good) The information sent is: AA 02 31 33 35 39 35 33 31 33 34 30 34 4F 60 59 7D. In Windows system, MultiByteToWideChar() can be called to convert the string into UNICODE encoded format.
  It is relatively simple to use this device to send text messages. One thing to note is that text messages cannot be sent too frequently. After successfully sending a text message, you need to wait for 2-3 seconds before sending the next one, otherwise it may cause the device to crash. Once the device crashes, it needs to be powered off and restarted.
  A more common type of device provides GSM Modem, which directly uses AT commands to send short messages. In the early 1990s, AT commands were only used for modem operations. Since there is no precedent for controlling mobile phone text messages, a protocol called SMS Block Mode was developed to fully control SMS (Short Message Service) through a terminal equipment (TE) or computer. A few years later, the major mobile phone manufacturers Nokia, Ericsson, Motorola and HP jointly developed a complete set of AT commands for GSM, including the control of text messages. The AT command evolved on this basis and was added to the GSM 07.05 [9] standard, and later the GSM 07.07 [10] standard. At present, there are three ways to realize the control of short messages: the original Block Mode; the Text Mode based on the AT command; the PDU Mode based on the AT command. Up to now, PDU has replaced Block Mode. It is relatively simple to use text mode, but it can only send ASCII codes and cannot send Chinese. The PDU mode is relatively complicated to develop, but has more powerful functions. For Chinese, UNICODE encoding is used for sending.
  AT stands for Attention, AT commands are a group of commands sent from TE (Terminal Equipment) or DTE (Data Terminal Equipment) to TA (Terminal Adapter) or DCE (Data Circuit Terminating Equipment) A set of commands that control the functions of MS (Mobile Station) to interact with GSM network services. Users can complete the control of calling SMS, phone book, data service, supplementary service, fax, etc. through AT commands.
  The AT standard is a line-oriented command language. In this application TE (Terminal Equipment Status), which can be any size computer, TA (Terminal Adapter), refers to a GSM modem. The command line consists of a string of alphanumeric characters that are sent to the modem to instruct the execution of the command specified by the characters. Transferred from bbs.sendsms.cn