Adaptor for isdn

The ISDN terminal Adapter, which has co-processor for controlling the communcation and NED (Network End Devices) includes a CombCODEC to transmit to converted analog voice signal to the telephone and the digital voice signal to the co-processor; a tone generator for generating the ring signal; a power converter for generating the telephone drive voltage; a user line relay circiut transmitting the telephone drive voltage to the telephone, relaying the voice signal between the telephone and combCODEC, and detecting the telephone hook state; a relay for transmitting the ring signal to the telephone; a tone decoder for decoding the DTMF signal, and transmitting it to the co-processor.