MC68HC908LJ12 Datasheet, PDF (95/413 Pages) Freescale Semiconductor, Inc – 8-bit microcontroller units

Oscillator (OSC)
The reference clock for the CGM, real time clock module (RTC), and
other MCU sub-systems is driven by the crystal oscillator. The COP
module is always driven by internal RC oscillator.
The RC internal oscillator runs continuously after a POR or reset and is
always available in run and wait modes. In stop mode, it can be disabled
by setting the STOP_IRCDIS bit in CONFIG2 register.
Figure 7-1. shows the block diagram of the oscillator module.
From SIM
CONFIG2
STOP_IRCDIS
EN
INTERNAL RC
OSCILLATOR
INTERNAL RC OSCILLATOR
CONFIG2
STOP_XCLKEN
MCU
CRYSTAL OSCILLATOR
OSC1
R_B
*R_S can be zero (shorted) when used with higher-frequency crystals.
Refer to manufacturer’s data.
X₁
See Section 23. for component value requirements.
C₁
ICLK
To SIM, COP
CGMRCLK
To CGM PLL
CGMXCLK
To RTC, ADC, LCD,
CGM Clock Selection MUX
OSC2
R_S*
C₂
Figure 7-1. Oscillator Module Block Diagram
Technical Data
96
Oscillator (OSC)
MC68HC908LJ12 — Rev. 2.1
Freescale Semiconductor