5.2.2 Internal Clock Sources

The device may be configured to use the internal oscillator block as the system clock by performing one of the following actions:

• Program the RSTOSC[2:0] bits in Configuration Words to select the INTOSC clock as the default system clock upon a device Reset.
• Write the NOSC[2:0] bits to switch the system clock source to the internal oscillator during run-time.

In INTOSC mode, OSC1/CLKIN is available for general purpose I/O. OSC2/CLKOUT is available for general purpose I/O or CLKOUT.

The function of the OSC2/CLKOUT pin is determined by the CLKOUTEN bit in Configuration Words.

The internal oscillator block has two independent oscillators that can produce two internal system clock sources.

1. The HFINTOSC (High-Frequency Internal Oscillator) is factory-calibrated and operates from 1 to 64 MHz. The frequency of HFINTOSC can be selected through the OSCFRQ Frequency Selection register, and fine-tuning can be done via the OSCTUNE register.
2. The LFINTOSC (Low-Frequency Internal Oscillator) is factory-calibrated and operates at 31 kHz.