The actual measurement shows that the communication distance in an open area is approximately 80 meters. The data manual states that when the AT pin is at a high level or left floating, it enters the AT mode; when it is at a low level, it enters the serial port transmission mode. However, the actual measurement shows that both the low-level AT and serial port transmission functions are present. By sending the corresponding AT+ command, the function can be activated. If the command is not AT+, it is assumed that the data will be transmitted through the serial port. Pulling up the AT pin will cause the module to malfunction.