ISDN interface unit

An integrated services digital network (ISDN) interface unit, connected to an ISDN line and a data processing unit having a memory, for interfacing between the data processing unit and the ISDN line, said interface unit comprising:

• a clock generating a clock signal;
• a DMA request signal generation circuit connected to the ISDN line by way of an ISDN connection circuit and generating direct memory access (DMA) request signals from the clock signal received from the clock to access the memory of the data processing unit;
• means for transferring one of pulse coded modulation (PCM) coded data from the ISDN to the memory of the data processing unit and PCM coded data stored in the memory of the data processing unit from the memory to the ISDN, in accordance with the DMA request signals generated by the DMA request signal generation circuit;
• an ISDN connection circuit connected to the ISDN line and executing a physical interface with the ISDN line, and when said ISDN connection circuit receives a digital signal from the ISDN line, said ISDN connection circuit processes the digital signal into a 64 kbps information channel signal including at least one of a voice signal, data information and a control channel signal;
• an ISDN connection control circuit, connected to said ISDN connection circuit and extracting and interpreting an ISDN connecting control message from the digital signal processed by and received from said ISDN connection circuit;
• and
• a personal computer interface circuit, connected to said ISDN connection control circuit and said DMA request signal generation circuit for executing an interface between the data processing unit and the integrated services digital network interface unit.