说明：  DHT21使用范例 //单片机 ： AT89S52 或 STC89C52RC // 功能 ：串口发送温湿度数据 晶振 11.0592M 波特率 9600 //硬件连接： P2.0口为通讯口连接DHT11,DHT11的电源和地连接单片机的电源和地，单片机串口加MAX232连接电脑
(DHT21 use examples //SCM: AT89S52 devices or STC89C52RC //function: serial send temperature and humidity data crystals 11.0592 M baud rate 9600 //hardware connection: P2.0 mouth to mouth, DHT11 DHT11 communication connection of power and the power of the single chip connected to a serial port, microcontroller and add MAX232 connecting a computer )