Non-return-to-zero (NRZ) encoding is a binary code in which the signal is neverat zero voltage. There is more energy in the wire compared to typical VOL/VOH digital logic,because there is always a voltage causing current to flow continuously. Energy is thefundamental property needed to communicate information over a distance. On a singlewire, voltages are measured relative to ground (e.g., RS232). On a twisted pair, voltagesare differential (e.g., RS422, USB). The binary values of 1 and 0 are encoded as positiveor negative voltage differences. In positive logic, 1 is a positive voltage difference and 0 isa negative voltage difference. In negative logic, the voltage representing 0 is higher thanthe voltage representing 1.
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