Psuedo Noise Generator Schematic

[Jim Patchell]

Magnus Danielson wrote:

> From: Jim Patchell <patchell at silcom.com>
> Subject: Psuedo Noise Generator Schematic
> Date: Wed, 06 Sep 2000 12:17:36 -0700
>
> Jim,
>
> >     As promised, I have done a quickie design that will go into a XC9536
> > cpld.  The features are selectable lenth of 9,18,27 or 36 bits.  This
> > has not been tested (or simulated for that matter), so......your milage
> > may differ.  If you spot any obvious problems, it would be nice if you
> > told me.  Here is the schematic:
> >
> >
> > http://www.silcom.com/~patchell/noise/noise.pdf
>
> OK. I reverse engineer out these polynoms:
>
>  9    5
> x  + x  + 1
>
>  18    6
> x   + x  + 1
>
>  27    5    2    1
> x   + x  + x  + x  + 1
>
>  36    24
> x   + x   + 1
>
> Now, for the polynomial form
>
>  n    m
> x  + x  + 1
>
> the polynomial
>
>  n    n-m
> x  + x    + 1
>
> is also correct.
>
> So, in one book I have n = 9 and m = 5 and in another I have n = 9 and m = 4,
> but these are equalent. m may also be 1 and 8.
>
> However, for n = 18 I have m = 7 in one book and m = 11 in the other, but these
> are equalent according to the rule. Your schematic does not match either of
> these. Actually, in other sources I have that m may be 3, 7, 9, 11 and 15.
>

    Check you count on this one.  I still count m=11.  I counted it in both
directions (but I am also not very good in the vision department).

>
> For n = 27 there is no valid polynom with only one tap, so we have to rely on
> multiple taps, and there you have a valid one.
>
> For n = 36 I have m as 9, 11, 15, 21, 25 and 27 but 24 is not allowed.
>

    This one I definately miscounted.

>
> So, as far as I have researched you have 2 out of 4. Move two taps and you
> should have a full house!
>
> Oh, if anyone wondered, there is no m for which you get a valid polynom when
> you have n to be 1024, that is a 1024 D flip-flops long shift register...
> I guess all you guys where sitting there and pondering about that, wheren't
> you? ;O)
>
> Cheers,
> Magnus