MAC7200 datasheet(521/976 Pages) FREESCALE

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MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

443

Chapter 24

Oscillator (OSC)

24.1

Introduction

The MAC7200 family of devices features an internal Automatic Level Control (ALC) oscillator. The

oscillator is designed for optimal startup margin with typical crystal oscillators. Selection of the oscillator

type is performed at Reset based on the value of the XCLKS pin.

After a Power on Reset (POR) or a system reset, the quality of the oscillation is checked by in the Clock

and Reset Generator (CRG) using the Clock Quality Checker before the oscillator is connected to the

internal system clocks. In the event that a stable oscillator output is not detected within a predefined time,

the MCU will be switched to its internal self clock mode.

Oscillator power is supplied from its own 3.3V PLL supply voltage generated by the Voltage Regulator in

order to minimize noise. The Oscillator continues to run in Doze mode.

A square wave input can be supplied to the device through the oscillator by connecting the external clock

source to the EXTAL pin with the Oscillator operating in External Clock mode.

Consult Chapter 23, “Clock and Reset Generator (CRG) for more information about the operation of reset

and clocks.

NOTE

The oscillators on the MAC71xx and MAC72xx are different designs. You

should characterize your oscillator design if you switch between the two

devices.

24.1.1

Features

The OSC_ALC_HIP7A contains the following features:

•

Low RF emissions with peak to peak swing limited dynamically.

•

Transconductance (gm) sized for optimum start-up margin for typical oscillators.

•

Integrated resistor eliminates the need for external bias resistor.

•

Low power consumption:

— Operates from 3.3 V (nominal) supply

— Amplitude control limits power

•

Oscillator reference output (fosc - ALC mode)

•

External clock input (fosc - External Clock mode)

•

Clock monitor

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