Freescale Semiconductor, Inc.
Pinout and Signal Descriptions
Signal Descriptions
NOTE: The internal return path for the oscillator is the VSSPLL pin. Therefore it
is recommended to connect the common node of the resonator and the
capacitor directly to the VSSPLL pin.
2 x E crystal or ceramic resonator
EXTAL
MCU
C1
C2
XTAL
Figure 3-4. Common Crystal Connections
NOTE: When selecting a crystal, it is recommended to use one with the lowest
possible frequency in order to minimise EMC emissions.
2 x E
EXTAL
CMOS-COMPATIBLE
EXTERNAL OSCILLATOR
MCU
XTAL
NC
Figure 3-5. External Oscillator Connections
XTAL is the crystal output.The XTAL pin must be left unterminated when
an external CMOS compatible clock input is connected to the EXTAL
pin. The XTAL output is normally intended to drive only a crystal. The
XTAL output can be buffered with a high-impedance buffer to drive the
EXTAL input of another device.
In all cases take extra care in the circuit board layout around the
oscillator pins. Load capacitances in the oscillator circuits include all
stray layout capacitances. Refer to Figure 3-4 and Figure 3-5 for
diagrams of oscillator circuits.
MC68HC912DG128 — Rev 3.0
Technical Data
Pinout and Signal Descriptions
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