MC68HLC908QY/QT Family — Rev. 2
Data Sheet
MOTOROLA
Oscillator Module (OSC)
93
Data Sheet — MC68HLC908QY/QT Family
Section 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 forth 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
11.3.1 Internal Oscillator
The internal oscillator circuit is designed for use with no external components to
provide a clock source with tolerance less than ±25% untrimmed. An 8-bit trimming
register allows adjustment to a tolerance of less than ±5%.
The internal oscillator will generate a clock of 4.0 MHz typical (INTCLK) resulting
in a bus speed (internal clock
÷ 4) of 1.0 MHz.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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