USB NRZI data encoding

[promach]

Why the following USB signalling bits do not seem to follow NRZI data encoding ?

[hexreader]

My guess is that you are looking at the "bits" field in your diagram rather than the waveforms at the top.

NRZI applies to the waveforms on the USB bus, not the data bits.

[promach]

what the spec labels "NRZI" is the signalling bits line in Sigrok, and what the spec labels "data" is the signalling symbols. ??

[hexreader]

My understanding of "symbols" is poor, but I see that user FVM has answered you on the edaboard forum. I trust him to have given the correct answer.

[voltsandjolts]

Cross ref to that post on edaboard:

https://www.edaboard.com/threads/usb-nrzi-data-encoding.394296/

[GeorgeOfTheJungle]

Low speed USB uses Manchester encoding IIRC.

[ataradov]

You can see from the capture that it is NRZI encoded. Even in the SYNC sequence you can see that 0 is encoded as a transition between the states, and for the last "1" in the SYNC the state remain "K".

[promach]

Low speed USB uses Manchester encoding or NRZI encoding ?

[ataradov]

All of them use NRZI with bit stuffing to prevent long runs of 1s. There is no Manchester anywhere in USB.  You can clearly see it on your log.