MC68HC908LJ24 Datasheet, PDF (105/464 Pages) Motorola, Inc – Microcontrollers

Oscillator (OSC)
Internal Oscillator
7.3 Internal Oscillator
The internal RC oscillator clock (ICLK) is a free running 64kHz clock (at
V_DD = 5V) that requires no external components. It is the reference clock
input to the computer operating properly (COP) module.
The ICLK can be turned off in stop mode by setting the STOP_IRCDIS
bit in CONFIG2. After reset, the bit is clear by default and ICLK is
enabled during stop mode.
7.4 X-tal Oscillator
The crystal (x-tal) oscillator circuit is designed for use with an external
32.768kHz crystal or ceramic resonator 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 7-1. 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)
The series resistor (R_S) is included in the diagram to follow strict Pierce
oscillator guidelines and may not be required for all ranges of operation,
especially with high frequency crystals. Refer to the crystal
manufacturer’s data for more information.
7.5 I/O Signals
The following paragraphs describe the oscillator I/O signals.
MC68HC908LJ24/LK24 — Rev. 2.1
Freescale Semiconductor
Oscillator (OSC)
Data Sheet
105