功能：当使P0^0脚为低电平时，单片机将向串口发送四分音符的中央do re mi fa sol la si，晶振：12Mhz，串口波特率：31.25kbps。-Function: When the P0 ^ 0 pin is low, the microcontroller will send serial port quarter notes Central do re mi fa sol la si, Crystal: 12Mhz, serial port baud rate: 31.25k