Motorola MCF5281, MCF5282 user manual Modes of Operation, Normal PLL Mode

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

9.1Features

Features of the clock module include:

•2- to 10-MHz reference crystal oscillator

•Support for low-power modes

•Separate clock out signal

9.2Modes of Operation

The clock module can be operated in normal PLL mode (default), 1:1 PLL mode, or external clock mode.

9.2.1Normal 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