Barry Gershenfeld wrote:
> As to conjectures about the dimming PWM, there are two factors I see that
> have to be kept in mind. One is that this product may be used at night, a=
nd
> the user may want to make the screen very dim.  So, while it seems to mak=
e
> sense that I don't really need 7 or 8 bits of resolution across the full
> brightness range, I may well need to run at 1% duty at the dim end, someh=
ow.
>
>
> Factor number two is that 1% at 200 Hz is 50us, and if I introduce a 10us
> disturbance into that pulse, it's wrong by 20%, and that will be visible =
as
> a flicker.
>
> I like the idea of the timers being used for the high and low portion of =
the
> cycle.  I even believe that it may be less important to keep the frequenc=
y
> exact, as long as the "on" duty time doesn't jump around.  That's relevan=
t
> because I'm concerned about reloading the timers to account for variable
> software overhead.
>  =20
You could set up a 10mS interrupt interval, and in the interrupt set up=20
a CCP to turn off the backlight after an appropriate delay.

PWM=3D750;
int_rtcc()
{
    turn on backlight;
    set CCP to turn off backlight in PWMuS;
}

Kerry

--=20
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