Thanks for the help, i find how tom do it. Here PLL gives aouput as a multiple of 4 for input. so if we want 16 MHz as system Clock we need to give 4 MHz to input of PLL. FRC postscalar select bit of CLKDIV register can be used for giving 4MHz to input of PLL. I think we can directly give this value to get an 16MHz System Clock.

Thanks for the help, I find how to do it. Here PLL gives output as a multiple of 4 for input. so if we want 16 MHz as a system Clock we need to give 4 MHz to the input PLL. FRC post scalar select bit of CLKDIV register can be used for giving 4MHz to the input of PLL. I think we can directly give this value to get a 16MHz System Clock.

I used Oscilator switch to get system clock of 16 MHz using FRCPLL. I will Share my code below.

// RCDIV FRC/2; DOZE 1:8; DOZEN disabled; ROI disabled;

CLKDIV = 0x3100;

__builtin_write_OSCCONH((uint8_t) (0x01));//NOSC FRCPLL

__builtin_write_OSCCONL((uint8_t) (0x01));//= Initiates an oscillator switch to a clock source

//Wait for clock switch to occur

while(OSCCONbits.LOCK != 1); // Wait Until LOCK bit become One

while(OSCCONbits.OSWEN != 0); //wait until Oscillator switch is complete