说明：  用P1.0输出1KHz和500Hz的音频信号驱动扬声器，作报警信号，要求1KHz信号响100ms，500Hz信号响200ms,交替进行，P1.7接一开关进行控制，当开关合上响报警信号，当开关断开告警信号停止
(1KHz and 500Hz with the P1.0 output signal driving the audio speaker for the alarm signal, requiring 1KHz signal ring 100ms, 500Hz signal sound 200ms, alternately, P1.7 take control of a switch, when switched on the sound alarm signal, when switch off warning signals to stop)