说明：  Holtek公司新近推出的DTMF电路HT9200A便是专用于电话联网控制的模块，它可以方便地与微控制器系统接口，以便组成智能型电话网络的测控系统
(Holtek company recently introduced is the DTMF Circuit HT9200A telephone network dedicated to the control module, which can be easily and micro-controller system interface to form intelligent telephone network control system)