说明：  DTMF双向收／发集成电路MT8880专门为双音频信号的收、发而设计，它既能产生发送双音频信号，又能对双音频信号进行接收译码，还能判断各种信号音(拨号音、回铃音、忙音)。以上就是它的应用电路和程序
(Two-way DTMF collection/fat MT8880 IC specifically for the dual audio signals received, the design, it could have sent dual audio signal, while the dual audio signal decoding receiver, but also to judge the sound signal (dial tone , ring back tone, busy tone). Above is its application circuit and procedures)