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Chapter 9
Clock Module
The clock module allows the MCF5282 to be configured for one of several clocking
methods. Clocking modes include internal phase-locked loop (PLL) clocking with either an
external clock reference or an external crystal reference supported by an internal crystal
amplifier. The PLL can also be disabled and an external oscillator can be used to clock the
device directly. The clock module contains:
• Crystal amplifier and oscillator (OSC)
• Phase-locked loop (PLL)
• Reduced frequency divider (RFD)
• Status and control registers
• Control logic
9.1
Features
Features of the clock module include:
• 2- to 10-MHz reference crystal oscillator
• Support for low-power modes
• Separate clock out signal
9.2
Modes of Operation
The clock module can be operated in normal PLL mode (default), 1:1 PLL mode, or
external clock mode.
9.2.1
Normal PLL Mode
In normal PLL mode, the PLL is fully programmable. It can synthesize frequencies ranging
from 2x to 9x the reference frequency and has a post divider capable of reducing this
synthesized frequency without disturbing the PLL. The PLL reference can be either a
crystal oscillator or an external clock.
MOTOROLA
Chapter 9. Clock Module
9-1
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