PXN20RM Datasheet, PDF (121/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

System Clock Description
EXTAL
3.3 V
3.3 V
4 – 40
MHz XTAL
OSCCLK
3.3 V
PLL
TRIMIRC
3.3 or 5 V
(V_RC)
16 MHz
IRC
XTAL
3.3 V
OSC32KEN
EXTAL32
3.3 or 5 V
(V_DDA)
32 kHz XTAL
TRIM128IRC
1.2 V
128 kHz
IRC
SYSCLKSEL
SYSCLKDIV
210
Clock
Switcher
+1,2,4,8,16
System Clock
XTAL32
3.3 or 5 V
(V_DDA)
Peripheral Clocks
Figure 5-1. PXN20 Available Clock Sources
5.1.3 External High-Frequency Crystal (4 – 40 MHz XTAL)
The 4 – 40 MHz XTAL clock uses an external high frequency crystal to provide the main clock source to
the circuit. The on-chip crystal oscillator has automatic level control and supports 4 MHz to 40 MHz
crystals. It can be used as external square-wave input.
A low power output buffer is selected automatically in Sleep mode to allow crystals of 8 MHz and below
to continue to run and clock the Real Time Clock (RTC) and Autonomous Periodic Interrupts (API).
A crystal in the full 4 – 40 MHz range can be kept enabled in Sleep mode to facilitate fast start up. In this
mode, the crystal oscillator cannot drive any internal modules (e.g.,RTC/ API), as the output driver is
disabled.
5.1.3.1 4 – 40 MHz XTAL Features
• Input frequency range: 4 MHz – 40 MHz
• Automatic level control
• Oscillator input mode 3.3V (V_DDSYN)
• External crystal mode enabled by default after reset. External square wave input supported, but
crystal bypass mode should be selected in startup code if an external crystal is not used.
• FMPLL reference clock
• Jitter < 0.5%, over one CAN frame
• Duty cycle: 40 – 60%
• Clock source capable of supporting FlexRay communications
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
5-3