Subscriber line interface circuitry with integrated serial interfaces

A method of communicating comprising:

• a) coupling a first device and a second device with a first unidirectional data line carrying data from the first device to the second device, a second unidirectional data line carrying data from the second device to the first device, and a clock line carrying a clock signal from the first device to the second device;
• and
• b) communicating frames of data serially between the first and second devices using the first and second unidirectional data lines, wherein frames communicated on the first unidirectional line have a first frame format, wherein frames communicated on the second unidirectional line have a second frame format, wherein individual timeslots of frames of the first and second formats are communicated substantially synchronously to the clock signal, wherein the first and second frame formats are distinct.