Patent ID: 6320883
Filing Date: 2001-11-20
Classification: H04Q

Abstract:
An automatic interface selection circuit for interfacing Integrated Services Digital Network (ISDN) equipment having a known reference point type with an ISDN service provider having an unknown reference point type, said interface selection circuit comprising:a) an analog detection circuit for electrically connecting to the ISDN service provider via an interface of the unknown reference point type so as to receive at least one sustained electrical signal from the ISDN service provider and thereby identify the unknown reference point type of the service provider based upon at least one characteristic of the electrical signal, said analog detection circuit comprising a voltage detection circuit coupled to at least one pin of the interface of said unknown reference point provided by the ISDN service provider so as to detect a voltage level of an electrical signal present on the at least one pin and thereby identify the reference point type of the connect ISDN service provider, said voltage detection circuit comprising:i) a zener diode connected to said at least one pin of said unknown reference point such that said zener diode conducts when the voltage level present at the pin exceeds a predetermined amount; andii) a current limiting resistor connected in relation with said zener diode to minimize degradation to a predetermined level of the signal on said unknown reference point when said zoner diode conducts; andb) a relay circuit coupled and directly responsive to said analog detection circuit to automatically switch and provide a compatible electrical connection between the known reference point type of the TSDN equipment and the unknown reference point type of the ISDN service provider.