# Sketch a waveform to show how the data 10101000 would be transmitted using NRZI encoding

• Comp Sci
Dan78
Homework Statement:
Using the grid below, sketch a waveform to show how the data 10101000 would be transmitted to line using Non-return-to-zero inverted (NRZI) line encoding. Assume the signal level is initially high as shown.
Relevant Equations:
None

Mentor
You need to show your attempt at this problem. I thought that I made that clear in my previous PM to you...

Dan78
Sorry. What i have is this

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• 2022-04-20 (1).png
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Mentor
Sorry. What i have is this
That looks close, but the "Inverted" part of NRZI means that you should invert that plot, no?

Homework Helper
Gold Member
That looks close, but the "Inverted" part of NRZI means that you should invert that plot, no?
I think the "I" is more complicated than that - it doesn't just invert the levels of NRZ, it is a completely different (and poorly named) edge-based system (an edge of either sign is a 1 and the absence of a signal edge on a clock pulse signifies a 0).

https://en.wikipedia.org/wiki/Non-return-to-zero#Non-return-to-zero_inverted
Edit: I don't normally like videos but this one is really clear:

Last edited:
Mentor
I think the "I" is more complicated than that - it doesn't just invert the levels of NRZ, it is a completely different (and poorly named) edge-based system
Interesting. I only briefly looked at the Wikipedia article for NRZI, which looked like simple inversion. I wonder if NRZ-I is different from NRZI... Guess I need to do some more reading...

pbuk
Homework Helper
Gold Member
Interesting. I only briefly looked at the Wikipedia article for NRZI, which looked like simple inversion. I wonder if NRZ-I is different from NRZI... Guess I need to do some more reading...
As I understand it NRZ-I and NRZ(I) are the same thing as NRZI: I have only ever seen it called NRZI (e.g. in the USB 2.0 specification) and importantly the "I" originally stood for IBM and was nothing to do with inversion (see http://ibm-1401.info/223-6988-729-MagTapeCE-InstRef-62-r.pdf).

This is totally different from NRZ, also called "on-off keying" where 1 is normally represented by a high voltage and 0 a low voltage: I am not aware of the opposite convention having a specific name, I suppose you could call it "Inverted NRZ" but that would just add to the confusion!

In summary

 Data 0​ Data 1​ ​ ​ L​ H​ NRZ​ ​ H​ L​ NRZ​ ​ No transition​ Transition (H-L or L-H)​ NRZI​ NRZ IBM​ Transition (H-L or L-H)​ No transition​ NRZI​ USB, USB 2​

Dan78
I have a starting point which is higher voltage level and every time when I encounter a 1 i have to change a voltage level. Hope is good now.

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• 2022-04-24.png
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pbuk