mc68hc908qf4 Freescale Semiconductor, Inc, mc68hc908qf4 Datasheet - Page 94

• Manufacturer Part Number: mc68hc908qf4
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Oscillator Module (OSC)
11.3.2 External Oscillator
11.3.3 XTAL Oscillator
Data Sheet
94
The external clock option is designed for use when a clock signal is available in the
application to provide a clock source to the microcontroller. The OSC1 pin is
enabled as an input by the oscillator module. The clock signal is used directly to
create BUSCLKX4 and also divided by two to create BUSCLKX2.
In this configuration, the OSC2 pin cannot output BUSCLKX4. So the OSC2EN bit
in the port A pullup enable register will be clear to enable PTA4 I/O functions on the
pin.
The XTAL oscillator circuit is designed for use with an external low-frequency
crystal or ceramic resonator to provide an accurate clock source. In this
configuration, the OSC2 pin is dedicated to the external crystal circuit. The
OSC2EN bit in the port A pullup enable register has no effect when this clock mode
is selected.
In its typical configuration, the XTAL oscillator is connected in a Pierce oscillator
configuration, as shown in
representation of the internal components and may not represent actual circuitry.
The oscillator configuration uses five components:
•
•
•
•
•
FROM SIM
Crystal, X
Fixed capacitor, C
Tuning capacitor, C
Feedback resistor, R
Series resistor, R
Freescale Semiconductor, Inc.
For More Information On This Product,
SIMOSCEN
MCU
Figure 11-2. XTAL Oscillator External Connections
OSC1
1
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Oscillator Module (OSC)
C
S
1
1
2
Figure
B
(can also be a fixed capacitor)
R
X
B
1
XTALCLK
11-2. This figure shows only the logical
BUSCLKX4
OSC2
R
C
S
2
TO SIM
BUSCLKX2
÷ 2
TO SIM
MC68HC908QF4 — Rev. 1.0
MOTOROLA