Freescale Semiconductor, Inc.
Internal Clock Generator Module (ICG)
8.5.6.2
8.5.6.3
8.5.7
Settling to Within 5 Percent . . . . . . . . . . . . . . . . . . . . . .130
Total Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130
Improving Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . .131
8.5.8
Trimming Frequency on the Internal Clock Generator . . . .133
8.6
8.6.1
8.6.2
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
8.7
8.7.1
Configuration Register Option . . . . . . . . . . . . . . . . . . . . . . . .135
EXTSLOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136
8.8
I/O Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136
ICG Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139
ICG Multiplier Register . . . . . . . . . . . . . . . . . . . . . . . . . . . .141
ICG Trim Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142
ICG DCO Divider Register . . . . . . . . . . . . . . . . . . . . . . . . .143
ICG DCO Stage Register . . . . . . . . . . . . . . . . . . . . . . . . . .144
8.8.1
8.8.2
8.8.3
8.8.4
8.8.5
8.2 Introduction
The internal clock generator module (ICG) is used to create a stable
clock source for the microcontroller without using any external
components. The ICG generates the oscillator output clock
(CGMXCLK), which is used by the COP, LVI, and other modules. The
ICG also generates the clock generator output (CGMOUT), which is fed
to the system integration module (SIM) to create the bus clocks. The bus
frequency will be one-fourth the frequency of CGMXCLK and one-half
the frequency of CGMOUT.
8.3 Features
The ICG has these features:
•
•
•
External clock generator, either 1-pin external source or 2-pin
crystal
Internal clock generator with programmable frequency output in
integer multiples of a nominal frequency (307.2 kHz ±25 percent)
Frequency adjust (trim) register to improve variability to ±2 percent
Advance Information
108
MC68HC908RFRK2
Internal Clock Generator Module (ICG)
MOTOROLA
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