MC68HC908GT16 Datasheet, PDF (110/412 Pages) Motorola, Inc – Microcontrollers

Internal Clock Generator (ICG) Module
7.5.5
7.5.6
7.5.6.1
7.5.6.2
7.5.6.3
7.5.7
Switching Internal Clock Frequencies . . . . . . . . . . . . . . . . 131
Nominal Frequency Settling Time . . . . . . . . . . . . . . . . . . . 132
Settling to Within 15 Percent . . . . . . . . . . . . . . . . . . . . . 132
Settling to Within 5 Percent . . . . . . . . . . . . . . . . . . . . . . 133
Total Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Trimming Frequency on the Internal Clock Generator . . . . 134
7.6 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
7.6.1 Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
7.6.2 Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
7.7 CONFIG2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
7.7.1 External Clock Enable (EXTCLKEN) . . . . . . . . . . . . . . . . . 136
7.7.2 External Crystal Enable (EXTXTALEN) . . . . . . . . . . . . . . . 137
7.7.3 Slow External Clock (EXTSLOW) . . . . . . . . . . . . . . . . . . . 137
7.7.4 Oscillator Enable In Stop (OSCENINSTOP) . . . . . . . . . . . 138
7.8 Input/Output (I/O) Registers . . . . . . . . . . . . . . . . . . . . . . . . . . 138
7.8.1 ICG Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
7.8.2 ICG Multiplier Register . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
7.8.3 ICG Trim Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
7.8.4 ICG DCO Divider Register . . . . . . . . . . . . . . . . . . . . . . . . . 144
7.8.5 ICG DCO Stage Register . . . . . . . . . . . . . . . . . . . . . . . . . . 145
7.2 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 low-voltage inhibit (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.
Finally, the ICG generates the timebase clock (TBMCLK), which is used
in the timebase module (TBM) and the computer operating properly
(COP) clock (COPCLK) which is used by the COP module.
Technical Data
110
MC68HC908GT16 • MC68HC908GT8 — Rev. 2
Internal Clock Generator (ICG) Module
MOTOROLA