AT command set
=============
This chapter will specifically describe how to use various AT commands.

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   * 

It is strongly recommended to read the following content before using the command to understand some basic information about the AT command.  

AT command classification
------------------

There are four types of generic AT commands:

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   * - Type 
     - Command format 
     - Instructions
   * - Test command
     - AT+<command name>=?
     - Query the internal parameters of the setting command and its value range
   * - query command
     - AT+<command name>?
     - Returns the current parameter value
   * - Set Command
     - AT+<command name>=<...> 
     - Set user-defined parameter values and run commands
   * - Execute command
     - AT+<command name>
     - Run commands without user-defined parameters

-  Not every AT command has the above four types of commands. 
-  Enter parameters in the command. Currently, only string parameters and shaping number parameters are supported. 
-  Parameters in angle brackets <> cannot be omitted. 
-  The parameters in square brackets [] can be omitted, and the default value is used when omitted. For example, some parameters are omitted when running the AT + WJAP command：
   ::

         AT+WJAP="ssid","password"
         AT+WJAP="ssid","password","11:22:33:44:55:66"

-  When there are still parameters to fill in after the omitted parameters, you must use ``,``，to show the separation. For example：
   ::
   
      AT+CWJAP="ssid","password",,1

-  Use double quotation marks to represent string parameters, For example：
   ::

      AT+CWSAP="ESP756290","21030826",1,4

-  Special characters need to be escaped, such as ``,``、``"``、``\`` and so on.

   -  ``\\``：Escape backslash. 
   -  ``\,``：Escape commas, commas separating parameters do not need to be escaped. 
   -  ``\"``：Escape double quotation marks, double quotation marks that indicate string parameters do not need to be escaped. 
   -  ``\<any>``：escape the ``<any>`` character, that is, only the ``<any>`` character is used, and no backslash is used. 

-  Only special characters in the AT **command** need to be escaped, and no escape is required elsewhere. For example, when the AT command port print ``>`` waits for input data, the data does not need to be escaped. 
   ::
      
      AT+WJAP="comma\,backslash\\ssid","1234567890"
      AT+MQTTPUB=0,"topic","\"{\"sensor\":012}\"",1,0

-  The default baud rate for the-AT command is  115200。
-  The length of each AT command should not exceed 256 bytes. 
-  AT command ends with a new line (CR-LF), so the serial port tool should be set to "new line mode". 
-  For the definition of AT command error code, please see :doc:`../instruction/other/error_code_`。