ram 68 for storing data is coupled to the dsp 70 the dsp is connected over appropriate conductors to integrated services digital network isdn chip 66 the isdn chip 66 is operatively coupled over appropriate conductor to analog logic circuit means 64 the analog logic circuit means 64 is connected to connector 62 whose output is to the transmission link which connects the adapter and the associated pc to an isdn network still referring to fig4 a message generated by an application program running in cpu 88 is transmitted through the comm port including i o controller 80 uart 76 processed in accordance with the teachings of the present invention and is delivered to the isdn chip 66 which the chip 66 provides one or more of the following isdn standard interfaces s or t or u the analog logic circuit means 64 provides over voltage protection impedance matching etc the connector 62 is the isdn standard connector rj45 fig4 a shows a block diagram for the alternate embodiment shown in fig3 a in fig4 a comm port 78 39 serial communication adapter and uart 76 39 are mounted under the covers of computer system 80 the isdn adapter 87 39 is mounted in extended box.