MC9S12P64VLHR Datasheet, PDF (241/566 Pages) Freescale Semiconductor, Inc – MC9S12P128 Reference Manual

7.4.5 External Oscillator
S12 Clock, Reset and Power Management Unit (S12CPMU)
7.4.5.1 Enabling the External Oscillator
An example of how to use the oscillator as Bus Clock is shown in Figure 7-34.
OSCE
EXTAL
UPOSC
Figure 7-34. Enabling the External Oscillator
enable external oscillator by writing OSCE bit to one.
crystal/resonator starts oscillating
UPOSC flag is set upon successful start of oscillation
OSCCLK
PLLSEL
Core
Clock
select OSCCLK as Core/Bus Clock by writing PLLSEL to zero
based on PLLCLK
based on OSCCLK
S12P-Family Reference Manual, Rev. 1.13
Freescale Semiconductor
241