MC908AP32CFBE Datasheet, PDF (75/324 Pages) Freescale Semiconductor, Inc – The following revision history table summarizes changes contained in this document. For your convenience, the page number designators have been linked to the appropriate location.

RC Oscillator
5.4 RC Oscillator
The RC oscillator circuit is designed for use with an external resistor and a capacitor.
In its typical configuration, the RC oscillator requires two external components, one R and one C.
Component values should have a tolerance of 1% or less, to obtain a clock source with less than 10%
tolerance. The oscillator configuration uses two components:
• C_EXT
• R_EXT
From SIM
To Clock Selection MUX
From SIM
SIMOSCEN
RCCLK
BUS CLOCK
CONFIG2
STOP_RCLKEN
EN
RC OSCILLATOR
MCU
See Chapter 22 for component value requirements.
OSC1
V_REG
R_EXT
C_EXT
OSC2
Figure 5-5. RC Oscillator
5.5 X-tal Oscillator
The crystal (x-tal) oscillator circuit is designed for use with an external 32.768kHz crystal to provide an
accurate clock source.
In its typical configuration, the x-tal oscillator is connected in a Pierce oscillator configuration, as shown
in Figure 5-6. This figure shows only the logical representation of the internal components and may not
represent actual circuitry. The oscillator configuration uses five components:
• Crystal, X₁ (32.768kHz)
• Fixed capacitor, C₁
• Tuning capacitor, C₂ (can also be a fixed capacitor)
• Feedback resistor, R_B
• Series resistor, R_S (optional)
MC68HC908AP Family Data Sheet, Rev. 4
Freescale Semiconductor
75