Developer Help

External Clock and Oscillator Modes

The Primary Oscillator (POSC) uses the OSC1 and OSC2 pins. POSC can be configured for an external clock input (EC mode), or an external crystal or resonator (XT or HS modes).

The clock frequencies associated with these modes are device dependent. Please see the specific device data sheet for details.

Code Example:

The following MPLAB^® XC16 compiler code example enables the Primary Oscillator as the default system clock and selects HS oscillator mode (supporting an external crystal) for a PIC24FJ128GA010 MCU:

#include <xc.h>

#pragma config FNOSC PRI        // Enable primary oscillator (XT, HS, EC)
#pragma config POSCMOD HS        // HS oscillator mode selected

int main(void)
{
    ...
}