AT指令一般应用于MT和TE程序间通信，即终端设备与PC应用之间的连接与通信。其对所传输的数据包大小有定义：即对于AT指令的发送，除AT两个字符外，最多可以接收1056个字符的长度（包括最后的空字符）。 -AT commands are commonly used for communication between MT and the TE program, the terminal equipment and the connection between PC applications and communications. Transmitted its packet size is defined: the AT commands for sending, in addition to AT two characters, but can receive up to 1056 characters in length (including the final null character.)