Signal Encoding - NRZI


Non-Return to Zero, Inverted (NRZI) Bit Encoding

Here, we see an example of signal encoding in Non-Return-To-Zero, Invert-on-one. NRZI uses a half-wave to encode each bit. Rather than transition through ground at each bit like Manchester encoding, NRZI uses the presence or absence of a transition to signify a bit (indicating a logical 1 by inverting the state).

The data being transmitted in this example is the hexadecimal byte "0E". First, the byte is broken down into four bit "nibbles", giving a nibble of "0" and a nibble of "E". Then, each nibble is looked up in a table to find the byte code associated with that hexadecimal number. The code for "0" hex is "11110" and the code for "E" hex is "11100". Finally, the byte codes are transmitted onto the wire using NRZI encoding.

For a discussion of the reasoning behind the association of four byte "nibbles" with five byte codes, refer back to the DATA ENCODING SECTION of this Fast Ethernet section.

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