HCS08 datasheet(94/290 Pages) MOTOROLA

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Internal Clock Generator (ICG) Module

MC9S08GB/GT

MOTOROLA

6.4 Initialization/Application Information

6.4.1 Introduction

The section is intended to give some basic direction on which configuration a user would want to select

when initializing the ICG. For some applications, the serial communication link may dictate the accuracy

of the clock reference. For other applications, lowest power consumption may be the chief clock

consideration. Still others may have lowest cost as the primary goal. The ICG allows great flexibility in

choosing which is best for any application.

The following sections contain initialization examples for various configurations.

NOTE:

Hexadecimal values designated by a preceding $, binary values designated by a

preceding %, and decimal values have no preceding character.

Important configuration information is repeated here for reference sake.

Table 6-4 ICG Configuration Consideration

Clock Reference Source = Internal

Clock Reference Source = External

FLL

Engaged

FEI

4 MHz < fBus < 20 MHz.

Medium power (will be less than FEE if oscillator

range = high)

Medium clock accuracy (After IRG is trimmed)

Lowest system cost (no external components

required)

IRG is on. DCO is on. (1)

NOTES:

1. The IRG typically consumes 100

µA. The FLL and DCO typically consumes 0.5 to 2.5 mA, depending upon output

frequency. For minimum power consumption and minimum jitter, choose N and R to be as small as possible.

FEE

4 MHz < fBus < 20 MHz

Medium power (will be less than FEI if oscillator

range = low)

Good clock accuracy

Medium/High system cost (crystal, resonator or

external clock source required)

IRG is off. DCO is on.

FLL

Bypassed

SCM

This mode is mainly provided for quick and reliable

system startup.

3 MHz < fBus < 5 MHz (default).

3 MHz < fBus < 20 MHz (via ﬁlter bits).

Medium power

Poor accuracy.

IRG is off. DCO is on and open loop.

FBE

fBus range <= 8 MHz when crystal or resonator is

used.

Lowest power

Highest clock accuracy

Medium/High system cost (Crystal, resonator or

external clock source required)

IRG is off. DCO is off.

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