"Random" Circuit Needed.
(On Fri, 03 Apr 2015 10:20:47 +1000, Jim Thompson
wrote:
On Thu, 02 Apr 2015 18:52:57 -0500, John Fields
wrote:
On 2 Apr 2015 10:42:50 GMT, Jasen Betts wrote:
On 2015-04-01, Jim Thompson
wrote:
On Thu, 02 Apr 2015 07:26:29 +1000, "David Eather"
wrote:
On Thu, 02 Apr 2015 05:14:13 +1000, Jim Thompson
wrote:
On Wed, 01 Apr 2015 15:07:54 -0400, Phil Hobbs
wrote:
On 04/01/2015 02:00 PM, Jim Thompson wrote:
For a simulation situation I need a random number generator with a
twist...
What I need to simulate is a "random" selection of one-of-16
outputs.
Clock "speed" is 12.5kHz ;-)
Built of 74HCxx parts is preferred... I have a full ensemble of
those
device in my PSpice library.
Thanks in advance.
...Jim Thompson
How random? You could use a 16-bit PRBS made from two HC299 and an
HC86. Feed back Q14 XOR Q13, and tap out four stages to a HC154
demux.
If you need better randomness, use four PRBSes of different
length.
Cheers
Phil Hobbs
I just need semi-random enough to test a fast AGC.
...Jim Thompson
there is a bias with the 8-bit just use the last 4 bit idea. With 255
'clocks' all states but 0000 will occur 16 times while 0000 will only
appear 15 - the cycle then repeats. The lack of the extra 0000 may
cause
the bias point to continually drift high.
I was wondering about that myself... I'll see if there's a cure.
r=(75*r+74)%65537 visits 0-65535 with no gaps.
not that i'd want to build it using 74LS logic.
---
But, if you had to, what would it look like, schematic-wise?
John Fields
smirk:-}
...Jim Thompson
Better(?) / easier is a Linear congruence generator- the simplest is s =
5*s + 1 (then mod 16) this outputs the sequence:
0
1
6
15
12
13
2
11
8
9
14
7
4
5
10
3
(multiply by 5 is just a shift right by 2 bits and an addition) + another
addition of 1
mod 16 is just throw away everything but the 4 LSB's
I still think LFSR is better - mod 65537 would be a bitch
|