PXD20 Datasheet, PDF (20/130 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

Overview
1.4.26 System clocks and clock generation modules
The system clock on the PXD20 can be derived from an external oscillator, an on-chip FMPLL, or the internal 16 MHz
oscillator.
The source system clock frequency can be changed via an on-chip programmable clock divider (1 to 2). An additional
programmable peripheral bus clock divider (ratios 1 to ) is also available.
The PXD20 has two on-chip FMPLLs (primary and secondary). Each features the following:
• Input clock frequency from 4 MHz to 16 MHz
• Lock detect circuitry continuously monitors lock status
• Loss Of Clock (LOC) detection for reference and feedback clocks
• On-chip loop filter (for improved electromagnetic interference performance and reduction of number of external
components required)
• Support for frequency ramping from PLL
The primary FMPLL module is for use as a system clock source. The secondary FMPLL is available for use as an alternate,
modulated or non-modulated clock source to eMIOS modules and as alternate clock to the DCU for pixel clock generation.
The main oscillator provides the following features:
• Input frequency range 4–16 MHz
• Square-wave input mode
• Oscillator input mode 3.3 V (5.0 V)
• Automatic level control
• Low power consumption
• PLL reference
The PXD20 also includes the following oscillators:
• 32 KHz low power external oscillator for slow execution, low power, and RTC
• Dedicated internal 128 kHz RC oscillator for low power mode operation and self wake-up
— ±10% accuracy across voltage and temperature (after factory trimming)
— Trimming registers to support improved accuracy with in-application calibration
• Dedicated 16 MHz internal RC oscillator
— Used as default clock source out of reset
— Provides a clock for rapid start-up from low power modes
— Provides a back-up clock in the event of PLL or External Oscillator clock failure
— Offers an independent clock source for the SWT
— ±5% accuracy across voltage and temperature (after factory trimming)
— Trimming registers to support frequency adjustment with in-application calibration
1.4.27 Periodic interrupt timer (PIT)
The PIT features the following:
• Eight general purpose interrupt timers
• Two dedicated interrupt timers for triggering ADC conversions
• 32-bit counter resolution
• Clocked by system clock frequency
PXD20 Microcontroller Data Sheet, Rev. 2
20
Preliminary—Subject to Change Without Notice
Freescale Semiconductor