Non-return-to-zero - Wikipedia, the free encyclopedia

acts "on a clock edge" or "during a clock cycle" since all transitions happen in the given amount of time representing the ... pulse amplitude modulation with polar.
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Non-return-to-zero - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/NRZI

Non-return-to-zero From Wikipedia, the free encyclopedia

(Redirected from NRZI) In telecommunication, a non-return-to-zero (NRZ) line code is a binary code in which "1s" are represented by one significant condition and "0s" are represented by some other significant condition, with no other neutral or rest condition. The pulses have more energy than a RZ code. Unlike RZ, NRZ does not have a rest state. NRZ is not inherently a self-synchronizing code, so some additional synchronization technique (perhaps a run length limited constraint, or a parallel synchronization signal) must be used to avoid bit slip.

The binary signal is encoded using rectangular pulse amplitude modulation with polar non-return-to-zero code

For a given data signaling rate, i.e., bit rate, the NRZ code requires only half the bandwidth required by the Manchester code. When used to represent data in an asynchronous communication scheme, the absence of a neutral state requires other mechanisms for data recovery, to replace methods used for error detection when using synchronization information when a separate clock signal is available. NRZ-Level itself is not a synchronous system but rather an encoding that can be used in either a synchronous or asynchronous transmission environment, that is, with or without an explicit clock signal involved. Because of this, it is not strictly necessary to discuss how the NRZ-Level encoding acts "on a clock edge" or "during a clock cycle" since all transitions happen in the given amount of time representing the actual or implied integral clock cycle. The real question is that of sampling--the high or low state will be received correctly provided the transmission line has stabilized for that bit when the physical line level is sampled at the receiving end. However, it is handy to see NRZ transitions as happening on the trailing (falling) clock edge in order to compare NRZ-Level to other encoding methods, such as the mentioned Manchester code, which requires clock edge information (is the XOR of the clock and NRZ, actually) and to see the difference between NRZ-Mark and NRZ-Inverted.

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Non-return-to-zero - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/NRZI

Contents 1 Unipolar Non-Return-to-Zero Level 2 Bipolar Non-Return-to-Zero Level 3 Non-Return-to-Zero Mark 4 Non-Return-to-Zero Space 5 Non-Return-to-Zero Inverted (NRZI) 6 Notes 7 See also 8 References

Unipolar Non-Return-to-Zero Level "One" is represented by one physical level (such as a DC bias on the transmission line). "Zero" is represented by another level (usually a positive voltage). In clock language, "one" transitions or remains high on the trailing clock edge of the previous bit and "zero" transitions or remains low on the trailing clock edge of the previous bit, or just the opposite. This allows for long series without change, which makes synchronization difficult. One solution is to only send bytes with lots of transitions, see RLL. The diagram shows a line representing the physical zero below the biased logical zero--showing the less usual case of "one" being a high voltage.

Bipolar Non-Return-to-Zero Level "One" is represented by one physical level (usually a negative voltage). "Zero is represented by another level (usually a positive voltage). In clock language, in bipolar NRZ-Level the voltage "swings" from positive to negative on the trailing edge of the previous bit clock cycle. An example of this is RS-232, where "one" is -5V to -12V and "zero" is +5 to +12V.

Non-Return-to-Zero Mark "One" is represented by a change in physical level. "Zero" is represented by no change in physical level. In clock language, the physical level transitions on the trailing clock edge of the previous bit to

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Non-Return-to-Zero Mark

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Non-return-to-zero - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/NRZI

represent a "one." No transition occurs for a "zero." When looking at the diagrams for transition-based encoding, it is important to realize that they might be inverted or partially inverted if the physical state were assumed to be the opposite just before the first bit in the diagram. This encoding is commonly referred to as just "NRZ" in other contexts[1]; FIPS 1037 also lists "non-return-to-zero change-on-ones" and "non-return-to-zero one" as encoding names that seem to mean the same thing.

Non-Return-to-Zero Space "One" is represented by no change in physical level. "Zero" is represented by a change in physical level. In clock language, the level transitions on the trailing clock edge of the previous bit to represent a "zero." This "change-on-zero" is used by High-Level Data Link Control and USB. They both avoid long periods of no transitions (even when the data contains long sequences of 1 bits) by using zero-bit insertion. HDLC transmitters insert a 0 bit after five contiguous 1 bits (except when transmitting the frame delimiter '01111110'). USB transmitters insert a 0 bit after six consecutive 1 bits. The receiver at the far end uses every transition -- both from 0 bits in the data and these extra non-data 0 bits -- to maintain clock synchronization. The receiver otherwise ignores these non-data 0 bits.

Non-Return-to-Zero Inverted (NRZI) Non return to zero, inverted (NRZI) is a method of mapping a binary signal to a physical signal for transmission over some transmission media. The two level NRZI signal has a transition at a clock boundary if the bit being transmitted is a logical one, and does not have a transition if the bit being transmitted is a logical zero. "One" is represented by a transition of the physical level.

Example NRZI encoding

"Zero" has no transition. Also, NRZI might take the opposite convention, as in USB signalling, when in Mode 1 (transition when signalling zero and steady level when signalling one). The transition occurs on the leading edge of the clock for the given bit. This distinguishes NRZI from NRZ-Mark.

NRZI-transition occurs for a zero

However, even NRZI can have long series of zeros (or ones if transitioning on "zero"), so clock recovery can be difficult unless some other encoding is used on top of it (such as RLL). Manchester encoding always reflects a clock edge, but it is less efficient than NRZI. NRZI encoding is used for recording on magnetic tape and for data transmission in the standard USB.

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Non-return-to-zero - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/NRZI

Note that USB injects a transition if 6 bits were the same.

Notes 1. ^ See, for instance, [1] (http://www.inetdaemon.com/tutorials/theory/modulation/non_return_to_zero.shtml)

See also Bipolar encoding Enhanced Non-Return-to-Zero-Level E-NRZ-L Return-to-zero Line code Universal asynchronous receiver transmitter

References Brey, Barry. The Intel Microprocessors, Columbus: Pearson Prentice Hall. ISBN 0-13-119506-9 Federal Standard 1037C in support of MIL-STD-188. Retrieved from "http://en.wikipedia.org/wiki/Non-return-to-zero" Categories: Line codes This page was last modified on 25 February 2008, at 23:12. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) tax-deductible nonprofit charity.

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