bit stuffing and nrz encoding

[vra...@imap1.asu.edu]

hi,
I am trying to do usb controller, with bit stuffing and nrz encodingin vhdl ,
i some how got the transmitter working, i seem to going no where in the
receiver,
can some body give me some ideas/suggest some web pages which give a good idea
about bit unstuffing and nrz decoding..

any help wud be appreciated

vijay
r...@asu.edu

[Andreas Koschak]

<vra...@imap1.asu.edu> wrote in message news:<Pine.GSO.4.21.020710...@general3.asu.edu>...

Well, if you wrote the transmitter, you should be able to design a
usable receiver as well.

Nevertheless, some important points / ideas:

- Note that the USB data stream is NRZI encoded. After you
bit-synchronized the data stream to your sample clock, go on and
sample in the middle of the bit. Use a register which is set at a
sample clock edge and reset at a data edge. so you should get the
right data. But you should know the encoding scheme from the
Transmitter.
- You may use 3-Point sampling. Use three Sample Clocks, store the
sampled data in 3 regs and store the result of the majority decision
(When two or more bits are 1, then the result is 1, else it's 0).
- Try to Re-Synchronize your Data clock at a data edge.

BTW: How do you synchronize to the NRZI signal?

Andreas Koschak
System Design Engineer
Liechti AG - Kriegstetten, Switzerland