Pseudo Random Noise

[Richard Martin]

>    Date: Fri, 15 Sep 1995 18:01:44 -0700
>    From: chordman at ix.netcom.com (Scott Gravenhorst, Synthaholic)
> 
>    I have logic maps for up to 31 bit pseudo random noise circuits.  I am 
>    interested in larger yet circuits (up to and beyond 64 bits).
> 

>From a XILINX application note entitled 'Linear Feedback Shift Registers':

 n    XOR Feedback from Outputs
--    --------------------------
 3	3,2
 4	4,3
 5      5,3
 6      6,5
 7      7,6
 8      8,6,5,4
 9      9,5
10	10,7
11	11,9
12	12,6,4,1
13	13,4,3,1
14	14,5,3,1
15	15,14
16	16,15,13,4
17	17,14
18	18,11
19	19,6,2,1
20	20,17
21	21,19
22	22,21
23	23,18
24	24,23,22,17
25	25,22
26	26,6,2,1
27	27,5,2,1
28	28,25
29	29,27
30	30,6,4,1
31	31,28
32	32,22,2,1
33	33,20
34	34,27,2,1
35	35,33
36	36,25
37	37,5,4,3,2,1
38	38,6,5,1
39	39,35
40	40,5,4,3

If the feedback is an XOR, the lockup state will be all zeroes.  If the
feedback is XNOR, the lockup state will be all ones.  These configurations
result in the maximum length sequence 2^n-1, but other configurations may
also result in the maximum length sequence.

A good reference book on the subject is Knuth's "The Art of Computer
Programming", Volume 2.  Unfortunately my copy is at home, but I'll check
tonight and see if there's any worthwhile information in there.

Other than the fact that I double checked my typing, I can't make any claims
as to the accuracy of the above information.  Use at your own risk.

Richard