M68HC08 Datasheet, PDF (108/230 Pages) Motorola, Inc – Microcontrollers

Oscillator Module (OSC)
8.5.2 Crystal Amplifier Output Pin (OSC2/PTA4/BUSCLKX4)
For the XTAL oscillator device, the OSC2 pin is the crystal oscillator
inverting amplifier output.
For the external clock option, the OSC2 pin is dedicated to the PTA4 I/O
function. The OSC2EN bit has no effect.
For the internal oscillator or RC oscillator options, the OSC2 pin can
assume other functions according to Table 1-3. Function Priority in
Shared Pins, or the output of the oscillator clock (BUSCLKX4).
Table 8-1. OSC2 Pin Function
Option
OSC2 Pin Function
XTAL oscillator
Inverting OSC1
External clock
PTA4 I/O
Internal oscillator
or
RC oscillator
Controlled by OSC2EN bit in PTAPUE register
OSC2EN = 0: PTA4 I/O
OSC2EN = 1: BUSCLKX4 output
8.5.3 Oscillator Enable Signal (SIMOSCEN)
The SIMOSCEN signal comes from the system integration module (SIM)
and enables/disables either the XTAL oscillator circuit, the RC oscillator,
or the internal oscillator.
8.5.4 XTAL Oscillator Clock (XTALCLK)
XTALCLK is the XTAL oscillator output signal. It runs at the full speed of
the crystal (f_XCLK) and comes directly from the crystal oscillator circuit.
Figure 8-1 shows only the logical relation of XTALCLK to OSC1 and
OSC2 and may not represent the actual circuitry. The duty cycle of
XTALCLK is unknown and may depend on the crystal and other external
factors. Also, the frequency and amplitude of XTALCLK can be unstable
at start up.
MC68HC908QY4•MC68HC908QT4•MC68HC908QY2•MC68HC908QT2•MC68HC908QY1•MC68HC908QT1
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Oscillator Module (OSC)
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