Hi Rodrigo

> fosc = 4MHz (internal oscillator) so,
> fosc / 4 = 1MHz
> 1MHz / 65536 = 15hz

Correct. Can you count the number of IRQs in, say, 10 seconds ?
You might find the IRQ is going off at (15/4)Hz or some other figure
that makes sense if there's a division bug

>   T1CON.NOT_T1SYNC = 1 ' not needed?

It's irrelevant with internal clocking

>   PIE1.TMR1IE = 1 ' enable overflow interrupt

Does mikrobasic account for banking ? PIE1 is in bank1

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