piclist 2001\08\16\181024a >
Thread: Generating a "truly" random number on the application of power
face BY : mikeTakeThisOuT@KILLspamwhitewing.co.uk

I think the best bet would be to time the WDT period against the
crystal/resonator, as this will vary slightly from part to part and
with voltage and temperature. Using TMR0, you can measure the period
to 1uS at 4MHz, i.e. about 0.005% of the nominal WDT period - it is
reasonable to assume that WDT periods will not be matched to this

I'd do it like this  :
On reset : Check STATUS to determine if reset was power-up or WDT:

If Power-up :   Set TMR0 to internal clock, no prescale.   Allow WDT to time out.

If WDT timeout :   TMR0 should contain a fairly random value, at least in the lowest
few bits.

If you want more randomness, increase the WDT prescaler setting, to
measure a longer measurement period. The TMR0 register may also have initialised randomly as well, which
will help.

On Tue, 14 Aug 2001 13:17:59 -0400, you wrote:

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See also: www.piclist.com/techref/microchip/math/index.htm?key=random
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Subject (change) Generating a "truly" random number on the application of power

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