Communication protocol between a communication device and an external accessory
 A method and apparatus for communicating both voice and control data between a communication device (such as a cellular phone) and an external accessory (such as a hands-free kit) over a data bus. The method includes formatting a sequence of bits into a repeating sequence of first time slots and second time slots, transmitting the voice data in the first time slot, and transmitting the control data in the second time slot. Notably, a first bit of each of the second time slots comprises a clock bit that alternates between a high value and a low value (e.g. a `1` or a `0`) as between consecutive second time slots. 
Qualcomm Incorporated
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Chienchung Hanchi David Steven C. George Robert Karthick Way-Shing James
Chang Huang Den Beste Pan Opalsky Chinnaswami Lee Hutchison