Abstract: A key telephone system (KTS) or a telephone private branch exchange (PBX) card is integrated into a personal computer to provide telephone system features. The telephone card includes a call controller, a switching network and an interface bus controller for coupling data signals between the PCI bus and an internal bus of the call controller whereby the telephone card is able to communicate with resources of the PC such as a LAN and a hard disk bulk memory for executing telecommunications functions. In this arrangement the PCI bus must carry both asynchronous data processing and control signals as well as reformatted synchronous signals. The addition of a synchronous bus for transporting synchronous signals is used to couple these signals between the switching network, a telephony features controller and the hard disk bulk memory. The use of the synchronous bus provides for improved telephone traffic capacity and PC functionality.