MC9S08GB60 Datasheet, PDF (110/290 Pages) Motorola, Inc – Microcontrollers

Internal Clock Generator (ICG) Module
When the ICG is in either FEI or SCM mode, XCLK is turned off. Any peripherals which can use XCLK
as a clock source must not do so when the ICG is in FEI or SCM mode.
7.4 Initialization/Application Information
7.4.1 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.
Table 7-4. ICG Configuration Consideration
FLL
Engaged
Clock Reference Source = Internal
FEI
4 MHz < f_Bus < 20 MHz.
Medium power (will be less than FEE if oscillator
range = high)
Good clock accuracy (After IRG is trimmed)
Lowest system cost (no external components
required)
IRG is on. DCO is on. ⁽¹⁾
Clock Reference Source = External
FEE
4 MHz < f_Bus < 20 MHz
Medium power (will be less than FEI if oscillator
range = low)
High 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 < f_Bus < 5 MHz (default).
3 MHz < f_Bus < 20 MHz (via filter bits).
Medium power
Poor accuracy.
IRG is off. DCO is on and open loop.
FBE
f_Bus 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.
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.
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.
MC9S08GB/GT Data Sheet, Rev. 2.3
110
Freescale Semiconductor