11 OSC - Oscillator Module

The oscillator module contains multiple clock sources and selection features that allow it to be used in a wide range of applications while maximizing performance and minimizing power consumption.

Clock sources can be supplied either internally or externally. External sources include:
  • External clock oscillators
  • Secondary Oscillator (SOSC)
Internal sources include:
  • High-Frequency Internal Oscillator (HFINTOSC)
  • Low-Frequency Internal Oscillator (LFINTOSC)
  • Analog-to-Digital Converter RC Oscillator (ADCRC)
Special features of the oscillator module include:
  • Oscillator Start-up Timer (OST): Ensures stability of the Secondary Oscillator’s 32.768 kHz crystal oscillator.
  • HFINTOSC Frequency Adjustment: Provides the ability to adjust the HFINTOSC frequency.

The Reset Oscillator (RSTOSC) Configuration bits determine the type of oscillator that will be used when the device runs after a Reset, including when the device is first powered up (see the table below).

Table 11-1. RSTOSC Selection Table
RSTOSCSFR Reset ValuesClock Source
COSCOSCFRQ
111111000 (1 MHz)EXTOSC per FEXTOSC
110110HFINTOSC @ 1 MHz
101101LFINTOSC
100100SOSC
011011Reserved
010010Reserved
001011Reserved
000000101 (32 MHz)HFINTOSC @ 32 MHz
If an external clock source is selected by the RSTOSC bits, the External Oscillator Mode Select (FEXTOSC) Configuration bits must be used to select the External Clock mode. These modes include:
  • ECL: External Clock Low Power mode
  • ECH: External Clock High Power mode

The ECH and ECL modes rely on an external logic-level signal as the device clock source. Each mode is optimized for a specific frequency range. The internal oscillator block produces both low-frequency and high-frequency clock signals, designated LFINTOSC and HFINTOSC, respectively. Multiple system operating frequencies may be derived from these clock sources.

The figure below illustrates a block diagram of the oscillator module.

Figure 11-1. Clock Source Block Diagram