DTMF（ Dual Tone Multi-Frequency ），即双音多频信号，是邮电业务的通信信令，它有很强的抗干扰能力，因此被广泛用于远距离通讯，如电话拨号通信中。基于单片机实现远距离DTMF信号的方法可以有多种，如用D/A转换器实现（基于PWM），也可用集DTMF信号的收发功能于一体的MT8880芯片等等。-DTMF (Dual Tone Multi-Frequency), the dual tone multi-frequency signals, signaling a Telecommunications Services of communication, it has a strong anti-interference ability, it is widely used for remote communications such as telephone dial-up communications. DTMF signal based on long-distance single chip can have a variety of ways, such as with the D/A converter to achieve (based PWM), can also be set DTMF signal transceiver functions in one of the MT8880 chip, and so on.