A bus connects a first and second integrated circuit. The bus includes a frame sync line which indicates the beginning of a frame when asserted, each frame containing a predetermined number time slots. A data out line provides data from the first to the second integrated circuit. The data represents the state of signals to be provided on output terminals of the second integrated circuit. Each of the data bits is assigned one of the time slots in the frame. A data in line provides a predetermined number of second data bits from the second to the first integrated circuit during each frame. Each of the second data bits is assigned one of the time slots and includes data including data bits indicating the state of input terminals of the second integrated circuit. A clock signal defines the time slots within the frame. The bus operates to provide frames substantially continuously between the first and second integrated circuit while the first and second integrated circuits.
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