MC68HC08LT8 Datasheet, PDF (51/156 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 5
Oscillator (OSC)
5.1 Introduction
The oscillator module provides the reference clocks for the MCU system and bus. Two oscillators are
running on the device:
• 1–16MHz crystal oscillator (OSC) — built-in oscillator that requires an external crystal or
ceramic-resonator. This oscillator drives the main bus and other MCU subsystems except the LCD
and PPI modules.
• 32.768kHz crystal oscillator (XTAL) — built-in oscillator that requires an external crystal or
ceramic-resonator. This oscillator drives the LCD and PPI modules.
5.2 Functional Overview
The X-tal oscillator circuit is designed for use with an external crystal or ceramic resonator to provide
accurate clock source.
In its typical configuration, the X-tal oscillator is connected in a Pierce oscillator configuration, as shown
in Figure 5-1. 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 & X₂
• Fixed capacitor, C₁ & C₃
• Tuning capacitor, C₂ & C₄ (can also be a fixed capacitor)
• Feedback resistor, R_B1 & R_B2
• Series resistor, R_S (for XTAL1 and XTAL2 only)
MC68HC08LT8 Data Sheet, Rev. 1
Freescale Semiconductor
51