MC908AP16CFAE Datasheet, PDF (75/324 Pages) Freescale Semiconductor, Inc – Table of Contents

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