> To get  a period of 250 out of TMR2 you set the PR2 register to 249!

And bingo, Bob's your uncle.
251/250 too long = 1 in 250 = 1 extra second per 4 minutes 10 seconds.
QED.

I think Bob, and Andrew Warren with a more general take on the same thing,
have hit the nail on the head.


        RM

> > > I initialized TMR2 with prescaler 4, postscaler 1:1 and period 250.
> > > ....
> > > clock lags behind about a second in 4 minutes. IMHO, the error is
> > > too big to fix it only in software. So there must be something else
> > > wrong.
> >

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