MC68HC908QY4_10 Datasheet, PDF (89/168 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Chapter 11
Oscillator Module (OSC)
11.1 Introduction
The oscillator module is used to provide a stable clock source for the microcontroller system and bus. The
oscillator module generates two output clocks, BUSCLKX2 and BUSCLKX4. The BUSCLKX4 clock is
used by the system integration module (SIM) and the computer operating properly module (COP). The
BUSCLKX2 clock is divided by two in the SIM to be used as the bus clock for the microcontroller.
Therefore the bus frequency will be one fourth of the BUSCLKX4 frequency.
11.2 Features
The oscillator has these four clock source options available:
1. Internal oscillator: An internally generated, fixed frequency clock, trimmable to ±5%.This is the
default option out of reset.
2. External oscillator: An external clock that can be driven directly into OSC1.
3. External RC: A built-in oscillator module (RC oscillator) that requires an external R connection only.
The capacitor is internal to the chip.
4. External crystal: A built-in oscillator module (XTAL oscillator) that requires an external crystal or
ceramic-resonator.
11.3 Functional Description
The oscillator contains these major subsystems:
• Internal oscillator circuit
• Internal or external clock switch control
• External clock circuit
• External crystal circuit
• External RC clock circuit
MC68HC908QY/QT Family Data Sheet, Rev. 6
Freescale Semiconductor
89