16-Bit Oscillator System: Fast RC Oscillator (FRC/LPFRC)

The FRC Oscillator is a fast (7.37 or 8 MHz nominal), user-trimmable, internal-RC oscillator. The output can drive the PLL or be divided using the programmable RCDIV bits.

Some devices contain an additional 500kHz Low-Power FRC (LPFRC) oscillator which enables lower-power consumption as compared with standard FRC oscillator.

The CLKDIV register RCDIV bits configure a selectable output divider that allows the choice of a lower clock frequency from seven different options plus, the direct FRC/LPFRC frequency output.

The FRC Oscillator Tuning register, OSCTUN, allows the user to fine tune the FRC/LPFRC Oscillator over a range of approximately ±12% (typical). Each bit increment or decrement changes the factory calibrated frequency of the FRC/LPFRC Oscillator by a fixed amount.


Code Example:

The following MPLAB® XC16 compiler code example enables FRCDIV as the default system clock source and sets the RCDIV divider bits to divide-by-16 at run-time for a PIC24FJ128GA010 MCU:

#include <xc.h>

#pragma config FNOSC FRCDIV    // Enable FRCDIV as system clock source
                    // default RCDIV setting sets FRC @ 4 MHz providing 4 MHz sys clk (2 MIPs)

int main(void)
    CLKDIVbits.RCDIV = 4;        // enable divide-by-16 setting
                        // sets FRC @ 0.5 MHz providing 0.5 MHz sys clk (0.25 MIPs)


Due to specified FRC accuracy, the FRC Oscillator modes may not meet the minimum frequency accuracy requirements for serial communications (such as UART and USB). Refer to the product family data sheet for more information about the FRC accuracy.

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