MC9S12XF512MLM Datasheet, PDF (193/1306 Pages) Freescale Semiconductor, Inc – S12X Microcontrollers

Chapter 5
Pierce Oscillator (S12OSCLCPV2)
Revision History
Revision Revision
Number Date
01.05 19-Jul-06
02.00 04-Aug-06
Author
Description of Changes
All xclks info was removed
incremented revision to match the design system spec revision
5.1 Introduction
The Pierce oscillator (XOSC) module provides a robust, low-noise and low-power clock source. The
module will be operated from the V_DDPLL supply rail (1.8 V nominal) and require the minimum number
of external components. It is designed for optimal start-up margin with typical crystal oscillators.
5.1.1 Features
The XOSC will contain circuitry to dynamically control current gain in the output amplitude. This ensures
a signal with low harmonic distortion, low power and good noise immunity.
• High noise immunity due to input hysteresis
• Low RF emissions with peak-to-peak swing limited dynamically
• Transconductance (gm) sized for optimum start-up margin for typical oscillators
• Dynamic gain control eliminates the need for external current limiting resistor
• Integrated resistor eliminates the need for external bias resistor in loop controlled Pierce mode.
• Low power consumption:
— Operates from 1.8 V (nominal) supply
— Amplitude control limits power
• Clock monitor
5.1.2 Modes of Operation
Two modes of operation exist:
1. Loop controlled Pierce (LCP) oscillator
2. External square wave mode featuring also full swing Pierce (FSP) without internal bias resistor
The oscillator mode selection is described in the Device Overview section, subsection Oscillator
Configuration.
MC9S12XF - Family Reference Manual, Rev.1.20
Freescale Semiconductor
193