On Tue, 21 Aug 2001 10:50:45 -0400, you wrote:

>Thanks Frank.
>
>>>>> Using TMR0 is ok when using RC oscillator. Don't use TMR0 in =
crystal
>operation.
>
>Why?
>
>In addition, some advised me to let the WDT time-out for the first time
>after power then get the TMR0. When I think about it, since the TMR0 is
>un-initialized upon powerup, is it really necessary to go through the =
WDT
>time-out?
Although TMR0's startup state is undefined, you may find that a batch
of chips could all come up with the same or similar values - using the
WDT's RC osc period should guarantee more variation between parts, as
other variables such as supply voltage (regulator tolerance) and
temperature will help shake things up. It's trivial to do, and will
undoubtably give a more intederminite result. Remember we are not
strictly after randomness, but a characteristic that is strongly
dependent on chip-to-chip variations. It doesn't matter if a chip
comes up with the same value every time, as long as this value stands
a good chance of being different from its neighbours.=20

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