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Abstract

One embodiment of the present invention provides a system for encoding a dataword into a current codeword within a stream of codewords, wherein each codeword in the stream has a substantially equal number of ones and zeros, and wherein each transition between codewords involves a substantially equal number of rising and falling transitions. The system creates the current codeword from the dataword and a preceding codeword in the stream by inverting substantially half of the zero bits of the preceding codeword and inverting substantially half of the one bits of the preceding codeword. This is accomplished by using the dataword to select one bits and the zero bits to invert; determining locations of the one bits and zero bits in the preceding codeword; and then inverting the selected one bits and zero bits in the preceding codeword to form the current codeword. Note that because the present invention balances rising and falling transitions without significantly increasing pin requirements, it achieves most of the electrical advantages of differential signaling along with most of the pin-efficiency of single-ended signaling. Moreover, by having substantially half the bits change at each transition, it is possible to determine timing information from transitions in the codeword, without the need for a separate clock signal.

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First Claim