LSFR

[Dev]

Hi all,


Could you pls explain what LSFR is ?
or where can I obtain some information on them.

thanks in advance

Dev

 

[Javier Castillo]

Hello:

I suppose you talk about a LFSR, a linear feedback shift register.
In hardware is primarily used for generate pseudo-random number sequences.

If you look in google LFSR you will find lot of information about them

Regards

Javier Castillo
(e-mail address removed)


(e-mail address removed) (Dev) wrote in @posting.google.com:

 

[Niels Bakker]

Helle Dev,,

LFSRs are used to create pseudo random sequences.
You can create a random sequence which repeats in 255 cycles with an 8
bits wide LFSR, by feeding certain bits in that register back to the
first bit. Usually done via an XNOR or XOR gate.

You can find the necessary tap-positions in the xapp052.pdf document of
Xilinx. (Google) or:

direct.xilinx.com/bvdocs/appnotes/xapp052.pdf

Good luck!

Niels Bakker

 

[Jonathan Bromley]

LFSRs are used to create pseudo random sequences.

But be careful...

LFSRs are quite good for creating random streams of
*bits*. They are rubbish for creating random
streams of *numbers*, because the LFSR register
value is highly correlated from one sample to the
next. If you want a new random *number* from an
LFSR, you must clock it as many times as there
are bits in your desired number.

LFSRs are great in hardware, because they map on
to such a simple and fast hardware structure. But
in a test fixture, the various linear-congruential
and other numerical recipes for random numbers are
likely to be more efficient, and will also provide
better-quality random numbers. The UNIFORM
procedure in IEEE.MATH_REAL does the job, and spares
you the very great pain of understanding the maths
--
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[M.A.Khader]

HI,

LSFR stands for Linear Feedback Shift Registers

Go to this link
http://www-math.cudenver.edu/~wcherowi/courses/m5410/m5410fsr.html

Regards,
A.khader

 

[Alain]

Hi,

Another link :
http://www.newwaveinstruments.com/r...uence_linear_feedback_shift_register_lfsr.htm

Regards

 

[Lukasz Salwinski]

But be careful...

LFSRs are quite good for creating random streams of
*bits*. They are rubbish for creating random
streams of *numbers*, because the LFSR register
value is highly correlated from one sample to the
next. If you want a new random *number* from an
LFSR, you must clock it as many times as there
are bits in your desired number.

well... If you search hard enough you'll actually
find a variation on the theme that actually
generates uniform distribution of *numbers*

lukasz

 

[vhdlcohen]

My site has an LFSR package in VHDL

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[Kholdoun TORKI]

Try this link. A great software utility running on Windows.

http://www.logiccell.com/~jean/LFSR/

Regards,
=================
Kholdoun TORKI
http://cmp.imag.fr
==================