MC9S08SG8 Datasheet, PDF (143/310 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 10
Internal Clock Source (S08ICSV2)
10.1 Introduction
The internal clock source (ICS) module provides clock source choices for the MCU. The module contains
a frequency-locked loop (FLL) as a clock source that is controllable by either an internal or an external
reference clock. The module can provide this FLL clock or either of the internal or external reference
clocks as a source for the MCU system clock. There are also signals provided to control a low power
oscillator (XOSC) module to allow the use of an external crystal/resonator as the external reference clock.
Whichever clock source is chosen, it is passed through a reduced bus divider (BDIV) which allows a lower
final output clock frequency to be derived.
The bus frequency will be one-half of the ICSOUT frequency.
10.1.1 Module Configuration
When the internal reference is enabled in stop mode (IREFSTEN = 1), the voltage regulator must also be
enabled in stop mode by setting the LVDE and LVDSE bits in the SPMSC1 register.
Figure 10-1 shows the MC9S08SG8 block diagram with the ICS highlighted.
MC9S08SG8 MCU Series Data Sheet, Rev. 0
Freescale Semiconductor
PRELIMINARY
143