Fully-integrated telephone unit

An integrated circuit forming a hands-free telephone unit for use in a digital telephone network and in association with an external keypad having a plurality of depressible key switches, an external microprocessor, an external microphone, and an external speaker, said integrated circuit comprising:

• keypad monitoring means arranged to be coupled to said external keypad for providing digital key code signals corresponding to the depression of said depressible key switches;
• audio processing means arranged to be coupled to said external microphone for converting outgoing analog voltages from said microphone representative of human speech to outgoing digital signals representative of said human speech and arranged for converting incoming digital signals from said network representative of human speech to incoming analog voltages representative of human speech and arranged to be coupled to said external speaker for providing said speaker with said incoming analog voltages;
• and
• digital interface means coupled to said audio processing means and said keypad monitoring means and arranged to be coupled to said digital network and said external microprocessor for conveying said incoming digital signals from said network to said audio processing means, said outgoing digital signals to said network, and said digital key code signals to said microprocessor,
• said digital interface means being arranged to be coupled to said network and said microprocessor by a serial bus, and wherein said digital interface means is arranged to convert parallel-bits of data to outgoing serial-bits of data and serial-bits of data to incoming parallel-bits of data.