System Clock Description
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 5-5
• Powered from internal 1.2 V
• Optionally disabled in Sleep mode
• Current consumption < 2 µA
• 128 kHz ±35% across process, voltage and temperature (before trimming)
• 128 kHz ±10% across voltage and temperature (after factory trimming)
• 128 kHz ±2% across voltage and temperature for a minimum duration of 100 ms (after application
trimming)
The internal 128 kHz RC oscillator is for low power mode operation and wake-up. It does not offer a
system clock source.
The 128 kHz_IRC clock can be optionally stopped to reduce current consumption in Sleep mode. See
Section 5.5.4, SWT Clock Domain.
5.1.6 External Low-Frequency Crystal (32 kHz_XTAL)
The PXN20 supports an external 32 kHz crystal oscillator to provide accurate wake-up and time-keeping
functions. The 32 kHz_XTAL clock is an external low power, high accuracy clock source to provide the
optional clock source for the RTC/API.
5.1.6.1 32 kHz_XTAL Features
• Two external pins required: EXTAL32 and XTAL32
• Supports external low frequency crystals in the range 32 kHz to 40 kHz
• Amplitude Level Control (ALC) to optimize power consumption
• Voltage and frequency filtering to guarantee clock frequency and stability
• Option to clock the API to provide a more accurate wakeup
• Option to clock the RTC to provide accurate time keeping
• Current consumption < 2 µA
• Powered from V
DDA
(3.3 V or 5 V)
• Can be disabled via software
5.1.7 FMPLL
The FMPLL module is one of the clock sources for the system clock. It is used especially for higher speed
run modes up to the maximum design speed of 128 MHz.
1
Its input clock is the undivided 4 – 40 MHz
XTAL.
5.1.7.1 FMPLL Features
• Input clock frequency range: 4 MHz to 40 MHz (on EXTAL)
1.Maximum speed for the current revision of silicon may be lower. See the PXN20 Microcontroller Data Sheet for
more information.
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