Okay.. this 4ns ( nano second / 1 X 10^-9) is really made my day.
It seem the timer make sense when multiply with 4ns.
At first, i tried to calculate Pulse-Width modulation Mode (PWM) for the timer1 of PIC24 but the period time is make no sense as i got 140us.
Coding to set your timer and interrupt :
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_T1IP=4; // set timer1 priority (4=dafault)
TMR1=0; //clear the time
PR1=34; //set the period register
T1CON=0x8020; //check T1CON register (Prescale set to 1:64)
_T1IF=0; //clear interrupt flag
_T1IE=1; //enable T1 interrupt source
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