MC9S12HY64 Datasheet, PDF (270/792 Pages) Freescale Semiconductor, Inc – S12 Microcontrollers

S12 Clock, Reset and Power Management Unit (S12CPMU) Block Description
7.4.5 External Oscillator
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
MC9S12HY/HA-Family Reference Manual, Rev. 1.04
270
Freescale Semiconductor