[Fwd: Re: [sdiy] Simplest random source]

[Magnus Danielson]

From: Seb Francis <seb at is-uk.com>
Subject: Re: [Fwd: Re: [sdiy] Simplest random source]
Date: Mon, 18 Nov 2002 03:51:59 +0000

> Do I understand right that this code only produces 1 random bit per cycle, so
> to get a 16bit random number you have to loop 16 times (16*19 instructions)?

Well, you are correct in that it only produces 1 random bit. As Harry said,
you then RC filter this on the output. Recall, if you run at 16 MHz, the
CPU cycle clock is at 4 MHz (assuming PIC16C71) then the bit-clock is up at
210 kHz and an RC filter at say 30 kHz would make a thick nice noise all the
way up there. It's bandwidth limited of course, but that is allways the case,
so why worry?

You can actually tap more bits straight out of it. Say just toss all of SHIFT7
onto a DAC. This would be similar to RC filtering actually, but the details is
a little bit beyond what what we should bare at this early time in the morning.

> Maybe it's a bit late at night and I'm not understanding it properly..

Well, you got the first part right, but not the way to get more bits.

Cheers,
Magnus