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Proposed merge[edit]

I agree to the mege of the Non-return-to-zero, inverted data here on the condition of resolution of the disputes about the data there.--Mancini 17:46, 27 November 2006 (UTC)

Agree. It is useful to have such closely related topics on the smae page. The NRZ page isn't too long anyway and there is already some of the NRZI info on it. -- Austin Murphy 14:23, 23 January 2007 (UTC)
Agree There is no point in keeping it alone. A redirect will do. mfx Q&A 11:27, 7 February 2007 (UTC)

I do not agree, they are two different codes, they should be referenced to each other under related topics, but not merged.

I also agree. -disgrutled EE student, 8 April 2007

Is this correct?[edit]

Taken from the article: "NRZ is used in the RS-232 serial protocol. Internal computer signals often use this code."

I don't believe this is correct. I was of the understanding that RS-232 used +12V to represent 0 and -12V to represent 1, and that was it. ...but at the same time, I don't want to post a correction because I could be mistaken.

According to my knowledge rs232 is not used for data encryption but only for the communication purposes beteen two devices it acts only as an controlled amplifier nothing else....
i know for sure NRZ is used in USB but in RS232 ????
NRZ (largely NRZ-L) is indeed used extensively in serial communications by network devices--Mancini 18:50, 22 November 2006 (UTC)

Response to queries[edit]

Just to respond to some of the points raise above:

  • RS-232/EIA-232 does indeed use ±12V to represent data with no null level, and so would quality as an NRZ scheme.
  • The page currently states that the "transmitter and receiver lack the timing synchronization". This is only true of NRZ if it is used with an asynchronous communication, and so is really a feature of the timing scheme, not the data representation scheme.
  • Regarding "DC blocking": I suspect that the author of this line may be referring to the fact that in a typical digital electronic system, the components generating the 0V and +V (representing 0 and 1) are CMOS transistors, which have a very small leakage current when not changing state, and so don't allow current to flow when the data isn't changing. If that's what the author meant, then this comment is superfluous. Such circuits still generate heat when they switch, and data loss is, in any case, highly unlikely.

--Gadget1700 17:09, 18 June 2006 (UTC)


I'm not sure is image Image:Nrz-i.gif correct; in the article Non-return-to-zero, inverted there's another image and it's different. First image shows that zero is represented by change of level, while in the article we can read "One" is represented by change in level, "Zero" is represented by no change in level.. Best,

I changed the NRZI definition, it was wrong. The image is correct. Mojodaddy 19:29, 18 December 2006 (UTC)

According to AMPR there's a differenc between NRZI and NRZ-I
BTW: I'm trying to find the correct terms for the german article about this - so tell there also if you find a exact source -- de:Benutzer:mik81 09:35, 1 March 2007 (UTC) -- 09:35, 1 March 2007 (UTC)
I thing I have an acceptable source. Look here: siemens
But convince yourself and search for "Nrz-i" nrzi inverted and get lots of hits
-- de:Benutzer:mik81 -- 09:52, 1 March 2007 (UTC)

NRZI definition[edit]

In NRZ-I encoding a '1' bit is represented by 0 volts or +V volts depending on the previous level. The encoding of '1' depends on the current state of the line If the previous voltage was 0 volts then the '1' bit will be represented by +V volts, however if the previous voltage was +V volts then the '1' bit will be represented by 0 volts. A '0' bit is represented by whatever voltage level was used previously.

This means that only a '1' bit can 'invert' the voltage, a '0' bit has no effect on the voltage, it remains the same as the previous bit whatever that voltage was. Rait 13:27, 2 March 2007 (UTC)

Alternative definitions[edit]

There do seem to be a number of different definitions of these data encoding schemes depending upon the manufacturer of the communications device. Back in the 1986 the Intel 82530 Technical User Manual had NRZ with a 1 as a high level and a 0 as a Low level, NRZI with a 1 as no change in level and 0 as a change in level. More recently the Motorola 68360 User Manual defines NRZ with a 1 as a high level and a 0 as a Low level, "NRZI Mark" with a 1 as no change in level and 0 as a change in level and "NRZI Space" with a 1 as a change in level and a 0 as no change in level. These do not entirely match what is on the main page. It is also worth noting that the hardware between the comms chip and the physical comms line may invert the signals - thus apparently inverting the output. Thus an encoded "high" will be represented by - 12volts and an encoded "low" by + 12volts on RS232 for example Commsguy (talk) 13:12, 16 September 2008 (UTC)

In the article there is no clear definition of NRZ-Mark; worse, it does not give a clear answer to the difference between NRZ-Mark and NRZI. From the images the two seems to be the same. There's something mentioned about the clock, but it's not clear for me (even though I did learn this stuff some time ago). Hoemaco (talk) 15:04, 12 October 2011 (UTC)


unipolar says:
"One is represented by one physical level (such as a DC bias on the transmission line).
Zero is represented by another level (usually a negative voltage)."
bipolar says:
"One is represented by one physical level (usually a positive voltage).
Zero is represented by another level (usually a negative voltage)."
which are really the same. Also from the image and the mention of On-Off Keying I'd guess that the unipolar should be when one level is zero volts.

Also, it says
"Disadvantages of an on-off keying are the waste of power due to the transmitted DC level"
which I'd contest. The DC level is a problem due to the spectrum and possible high-pass media, but not because of the power. Actually OOK is the best for power saving, as there's no power transmitted for zeros, ie. roughly half the time.
Hoemaco (talk) 08:23, 10 March 2012 (UTC)

Nrz-s.gif misleading[edit]

The Nrz-s.gif has a bit pattern labeled on top as "101100011010". The misleading aspect is the first bit which should be unknown or a 'X'. The gif does not show the previous low state. Alternatively, the gif could be edited to omitted that first '1', leaving just a fraction of the first bit's end of low state. — Preceding unsigned comment added by (talk) 22:56, 9 May 2013 (UTC)