12.4.4 Internal Fast RC (FRC) Oscillator

The dsPIC33A devices contain one instance of the Internal Fast RC (FRC) Oscillator. The FRC provides a nominal 8 MHz clock without requiring an external crystal or ceramic resonator, which results in system cost savings for applications that do not require a precise clock reference. The application software can tune the frequency of the oscillator using the TUN[5:0] bits in the FRC Oscillator Trim register FRCTUN. The FRC oscillator can be enabled or disabled by the FRCEN bit in the OSCCTRL register and is ready when the FRCRDY bit is set in the OSCCTRL register. The FRC is always enabled after any Reset.

The Internal FRC Oscillator starts quickly. Unlike a crystal oscillator, which can take several milliseconds to begin oscillation, the Internal FRC starts oscillating immediately.