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Chapter 8 S12 Clock, Reset and Power Management Unit (S12CPMU_UHV_V6)
MC9S12ZVM Family Reference Manual Rev. 1.3
Freescale Semiconductor
297
8.4.5
External Oscillator
8.4.5.1
Enabling the External Oscillator
An example of how to use the oscillator as source of the Bus Clock is shown in
Figure 8-39. Enabling the external oscillator
PLLSEL
OSCE
EXTAL
OSCCLK
Core
enable external oscillator by writing OSCE bit to one.
crystal/resonator starts oscillating
UPOSC
UPOSC flag is set upon successful start of oscillation
select OSCCLK as Core/Bus Clock by writing PLLSEL to zero
Clock
based on PLL Clock
based on OSCCLK