说明：  SPI接口的ADS7816，其输出数据的格式是最高有效位(B11位)在前,当最低有效 位(B0位)输出后,若CS变为高电位,则一次转换结束,最高转换速度200kHz
(。-This is the serial AD acquisition of reading and writing chip ADS7816 procedure for the Keil compilerthe output data format is the most significant bit (B11-bit) in the former, when the least significant bit (B0-bit) output, if the CS becomes high potential, then the end of a conversion, the maximum conversion rate of 200kHz)