MC908QY8CDWE Datasheet, PDF (95/232 Pages) Freescale Semiconductor, Inc – Addendum to MC68HC908QB8, rev. 3

Chapter 11
Oscillator Module (OSC)
11.1 Introduction
The oscillator (OSC) module is used to provide a stable clock source for the MCU system and bus.
The OSC shares its pins with general-purpose input/output (I/O) port pins. See Figure 11-1 for port
location of these shared pins. The OSC2EN bit is located in the port A pull enable register (PTAPUEN)
on this MCU. See Chapter 12 Input/Output Ports (PORTS) for information on PTAPUEN register.
11.2 Features
The bus clock frequency is one fourth of any of these clock source options:
1. Internal oscillator: An internally generated, fixed frequency clock, trimmable to ± 0.4%. There are
three choices for the internal oscillator,12.8 MHz, 8 MHz, or 4 MHz. The 4-MHz internal oscillator
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 XTAL oscillator that requires an external crystal or ceramic-resonator.
There are three crystal frequency ranges supported, 8–32 MHz, 1–8 MHz, and 32–100 kHz.
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
MC68HC908QB8 Data Sheet, Rev. 3
Freescale Semiconductor
93