Fujitsu F2MC-16LX Hardware Manual page 39

CHAPTER 1 OVERVIEW
Caution on Operations during PLL Clock Mode
Even if the oscillator comes off or the clock input stops with the PLL clock selected for this
microcontroller, the microcontroller may continue to operate at the free-running frequency of the PLL
internal automatic oscillator circuit. Performance of this operation, however, cannot be guaranteed.
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