MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 311
Chapter 6Pierce Oscillator (S12XOSCLCPV1)

6.1 Introduction

The Pierce oscillator (XOSC) module provides a robust, low-noise and low-power clock source. The
module will be operated from the VDDPLL supply rail (2.5 V nominal) and require the minimum number
of external components. It is designed for optimal start-up margin with typical crystal oscillators.

6.1.1 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
Low power consumption:
Operates from 2.5 V (nominal) supply
Amplitude control limits power
Clock monitor

6.1.2 Modes of Operation

Two modes of operation exist:
1. Loop controlled Pierce oscillator
2. External square wave mode featuring also full swing Pierce without internal feedback resistor