Datasheet

Oscillator (OSC)
MC68HC908AP Family Data Sheet, Rev. 4
76 Freescale Semiconductor
Figure 5-6. Crystal Oscillator
The series resistor (R
S
) is included in the diagram to follow strict Pierce oscillator guidelines and may not
be required for all ranges of operation, especially with high frequency crystals. Refer to the crystal
manufacturer’s data for more information.
5.6 I/O Signals
The following paragraphs describe the oscillator I/O signals.
5.6.1 Crystal Amplifier Input Pin (OSC1)
OSC1 pin is an input to the crystal oscillator amplifier or the input to the RC oscillator circuit.
5.6.2 Crystal Amplifier Output Pin (OSC2)
When the x-tal oscillator is selected, OSC2 pin is the output of the crystal oscillator inverting amplifier.
When the RC oscillator or internal oscillator is selected, OSC2 pin is the output of the internal bus clock.
5.6.3 Oscillator Enable Signal (SIMOSCEN)
The SIMOSCEN signal from the system integration module (SIM) enables/disables the x-tal oscillator, the
RC-oscillator, or the internal oscillator circuit.
C
1
C
2
R
B
X
1
R
S
MCU
OSC2OSC1
See Chapter 22 for component value requirements.
SIMOSCEN
From SIM
STOP_XCLKEN
CONFIG2
XCLK
To Clock Selection MUX
32.768kHz