PIC32MZ Oscillator - Primary Oscillator

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 (HS mode).

#pragma config POSCMOD = EC  //default = external clock
#pragma config POSCMOD = HS  //default = high-speed crystal

External Clock Mode with Output Clock


When POSC is in the EC mode, the OSC1 pin is a high-impedance input that can be driven by a CMOS driver.

The EC mode also disables the internal feedback buffer allowing the OSC2/CLKO pin to be used for other functions (general purpose I/O or as a clock out). The output clock provided on the CLKO pin is the peripheral bus clock number 1 (PBCLK1) divided by 2.

#pragma config OSCIOFNC = ON  // clock out enabled
#pragma config OSCIOFNC = OFF // clock out disabled

USB Input Clock Requirements


If using the USB peripheral, POSC must be 12 MHz or 24 MHz. You must also configure the USB PLL for a 12 MHz or 24 MHz input frequency.

#pragma config UPLLEN = ON            // Enable USB PLL
#pragma config UPLLFSEL = FREQ_12MHZ  // USB PLL input clock = 12MHz
#pragma config UPLLFSEL = FREQ_24MHZ  // USB PLL input clock = 24MHz
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