Datasheet

Appendix: Information on MC68HC912DT128A Mask Set Changes
Oscillator – Minor Changes
MC68HC912DT128A — Rev 4.0 Technical Data
MOTOROLA Appendix: Information on MC68HC912DT128A Mask Set Changes 459
24.7 Oscillator – Minor Changes
The Automatic Level Control (ALC) capacitor reference was changed
from VDD to VSS in the crystal oscillator circuit to improve noise
immunity.
Parasitic capacitance on internal signal lines has been decreased, thus
decreasing sensitivity to external capacitance changes.
NOTE: For best oscillator performance, it is recommended that the load
capacitor selection is verified on changing to the new mask.
A reduction was made to the gain of the Operational Transconductance
Amplifier (OTA) to reduce the amplification of any noise on the EXTAL
pin.
24.8 PLL
The limp Home clock frequency has been re-alligned to the specification
values to reduce sensitivity to system noise and hence reduce PLL jitter.
Note: It is advisable to verify the XFC filter components and PLL lock
time due to the above changes.
VCO start-up will now be at the minimum frequency whilst the power up
sequence of the current controlled oscillator has been improved.
The XFC pin is now preconditioned to VDDPLL when PLL is deselected
so XFC doesn’t float. This ensures the PLL starts up at low frequency
and ramps up to the desired frequency.
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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