On 2015-04-16, rickman wrote:
On 4/15/2015 7:38 PM, John Fields wrote:
On Thu, 02 Apr 2015 17:20:47 -0700, 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
---
Amazing, isn't it?

Idiots with opinions post their garbage as if it was holy but post
no evidence to support their claims.

I don't know that Jim is an idiot, but I'm not sure this formula is very
useful to implement in logic easily. The multiply is not too bad and
the addition is easy. But the modulo operation by 2^16+1 is downright
hard. I think that is why he is smirking. He knows this is not very
practical...

The modulo is easier than the multiply.

one 16 bit - 7 bit subtract
one 16 bit + 0 bit add with carry.



--
umop apisdn