MC912DG128A Motorola, MC912DG128A Datasheet - Page 379

• Manufacturer Part Number: MC912DG128A
• Description: Microcontrollers
• Manufacturer: Motorola

What Do I Do In
Case The
Oscillator Does
Not Start-up?
3-cgmpa
MOTOROLA
2. Using VDDPLL=VSS (i.e. shutting off the PLL). Doing so
3. Also, placing a high value resistor (>1M ) across the EXTAL and
1. First, verify that the application schematic respects the principle of
2. Re-consider the choice of the tuning capacitors.
3. If the quartz or resonator is of a high frequency type (e.g. above
4. The oscillator circuitry is powered internally from a core VDD pad
5. If possible, consider using a resonator with built-in tuning
smaller. The consequently smaller current will be reached with a
larger ‘extal’ swing.
increases the starting current by approximately 50%. All other
parameters staying the same, a larger ‘extal’ swing will be required
to reduce this starting current to its quiescent value.
XTAL pins significantly increased the oscillation amplitude.
Because this complicates the design analysis as it transforms a
pure susceptance j C1 into a complex admittance G+j C1,
Motorola cannot promote this application trick.
operation, i.e. crystal mounted between EXTAL and VSS,
Capacitor C1 between XTAL and EXTAL, Capacitor C2 between
XTAL and VSS, nothing else. This is not the conventional MCU
application schematic of the Pierce oscillator as it can be seen on
other HC12 derivatives!
10MHz), consider using VDDPLL=0V. Obviously, this choice
precludes the use of the PLL. However, in this case the oscillator
circuitry has more quiescent current available and the starting
transconductance is thus significantly higher.
and the return path is the VSSPLL pad. Verify on the application
PCB the correct connection of these pads (especially VSSPLL),
but also verify the waveform of the VDD voltage as it is imposed
on the pad. Sometimes external components (for instance choke
inductors), can cause oscillations on the power line. This is of
course detrimental to the oscillator circuitry.
capacitors. They may offer better performances with respect to
their discrete elements implementation.
Appendix B: CGM Practical Aspects
A Few Hints For The CGM Crystal Oscillator Application
Appendix B: CGM Practical Aspects
MC68HC912DT128A Rev 2.0
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