Thanks all guys ( Bob, Olin and Joe in mail receiving order )
As usual, language bariers have stopped me to put the right question.

Bob, I need a finest resolution so every time the minimum period will be
10 seconds and no more, for 10 minutes and 10% I need to do 60 times 1
second on and 9 secons off.

Olin and Joe, I'm using an internal RTC ( interrupt tmr0 based ) which is
self running only in the task I need ( by activating or not the
interrupts). There is no problem here, I'm using flags and semaphores.
This RTC is used to display a decreasing time clock from 9.59
 ( 9 minutes and 59 seconds ) to 0.00.
The flow of that clock is permanent in the phase I'm talking about even
the output command is not because in the same task I need to command an
output nibble with the algorithm I was talking about.
My ideea is to forget about the minutes and to read the seconds every time
I want an output command.
 Then keeping the command ON a number of seconds equal with percentage/10
and OFF the number of seconds equal with ( 100 - percentage )/10 ,
should provide the output I need... But how to deal with a 0 second reading
 ( for example at 3.00 ) ? I could test the seconds and if are 0 to wait until
are changing...

I think this is the partial answer for my problem... there is an easyest
way ?

Thank you,
Vasile


On Mon, 1 Apr 2002, Olin Lathrop wrote:

> > I have a problem here: I'm trying to understand a methode for switching
> > on and off one pic output respecting an input percentage proportion from
> > 10% to 90% of a pre-programmed time value ( from 10 seconds to 10 minutes
> > ). With other words:
> > 10% from 10 seconds means 1 second on + 9 seconds off
> > 10% from 10 minutes means 60 x ( 1 second on + 9 secons off)
> > ...
> > 90% from 5 minutes and 30 seconds means 33 x (9 seconds on + 1
> > second off)
> >
> > How I can define a common algorithm which fits on any time and any
> > percentage ?
>
> This sounds simple if you rephrase it as a PWM output lasting for a
> specified time.  Since your PWM period is 10 seconds, this is simple to do
> in software.  If 10% resolution is enough, then you only need an interrupt
> every second to re-evaluate the PWM output.
>
> I think you already know this, Vasile, so what am missing?
>
>
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