ISDN terminal adapter with SCSI interface

This paper describes the development of an Integrated Services Digital Network (ISDN) terminal adapter (TA) card which conforms to CCITT Rec. I.430, I.441 and I.451. The TA card has a full function analogue port to accommodate a conventional analogue line equipment and also a SCSI based communication interface for a modern high speed microcomputer or workstation host machine. A transformerless ringing current generator using a switch mode regulator was also designed and incorporated in the analogue port to make the TA very compact. Two microcomputers equipped with the TA cards were able to communicate with each other over an ISDN connection which teleconversation between two analogue telephones connected to the same TA cards was in progress.