Datasheet

MC68HC908QY4•MC68HC908QT4•MC68HC908QY2•MC68HC908QT2•MC68HC908QY1•MC68HC908QT1
102 Oscillator Module (OSC) MOTOROLA
Oscillator Module (OSC)
NON-DISCLOSURE AGREEMENT REQUIRED
8.2 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 forth of the BUSCLKX4
frequency.
8.3 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.
8.4 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