说明：  双音多频（DTMF）信号的生成以及检测程序，在电话拨号中使用了该原理，文件1位6位号码生成及识别，文件2为8位号码生成和识别。
(Dual tone multi-frequency (DTMF) signal generation and detection procedures, the use of the principle in the telephone dial, file 1 6 number generation and identification, file 2 for 8 number generation and identification.)