Fujitsu F2MC-8FX Hardware Manual page 91

CHAPTER 6 CLOCK CONTROLLER
Note:
If you use only the main clock without using subclock oscillation on a two-system clock product and it enters
subclock mode for some reason, there is no solution to recovering its operation as there is no clock supply
available. If you use the main clock alone, therefore, be sure to select a single system clock product.
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