Abstract: A telecommunications system is provided to connect a plurality of dissimilar types of subscriber telecommunications devices and to provide integrated telecommunications services. The system is provided with a digital communications link comprising a PCM bus for voice and data and an HDLC coded PCM highway for control signals to create a master slave environment, wherein a central processing board operates as a master processor for a plurality of peripheral processor boards. The peripheral boards are coupled to various subscriber telecommunications devices. The CPU board is provided with hierarchical program control that includes low level program code for driving CPU board components, and mid-level program code for effecting system functions and CPU board functions. The mid-level code can also be used to create data bases relating to system configuration as well as data bases for each port associated with the peripheral boards.