PIC32MX Oscillator - Reference Clock

Last modified by Microchip on 2023/11/10 11:08


Reference clock diagram

The Reference Clock can be used to drive the Serial Peripheral Interface (SPI) peripheral or to generate a clock on the Reference Clock Output (REFCLKO) pin.

The reference clock can be derived from any of the following clock sources: System Phased-Lock LoopPrimary OscillatorFast RCLow-Power RCUSB Phased-Lock Loop output (96 MHz)Secondary OscillatorSystem ClockPeripheral Bus Clock, and Reference Clock input.

Each reference clock has a high-precision divider based on this formula:

Reference clock high-precision divider formula

  • refOscDiv can be any integer from 1 to 32768,
    • when refOscDiv = 0, the output clock = the input clock.
  • trimValue can be any integer from 1 to 512.
// ref clock base = FRC
// disable ref clock
PLIB_OSC_ReferenceOscDisable(OSC_ID_0, OSC_REFERENCE_1);
// enable ref clock
PLIB_OSC_ReferenceOscEnable(OSC_ID_0, OSC_REFERENCE_1);
// refOscDiv = 32768
PLIB_OSC_ReferenceOscDivisorValueSet (OSC_ID_0, OSC_REFERENCE_1, 32768);
// trimValue = 256
PLIB_OSC_ReferenceOscTrimSet(OSC_ID_0, OSC_REFERENCE_1, 256);
// ref clock is driven out REFCLKO pin
PLIB_OSC_ReferenceOutputEnable(OSC_ID_0, OSC_REFERENCE_1);