FUJITSU F2MCTM-16LX - Manual (Page 109)

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CHAPTER 5 CLOCKS
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Machine clock
The machine clock controls the operation of the CPU and peripheral functions. One cycle of machine clock
is regarded as one machine cycle (1/
φ). An operating machine clock can be selected from among the main
clock, sub-clock, and five types of PLL clock.
Note:
When the operating voltage is 5 V, the oscillation clock can be between 3 MHz and 16 MHz. When an
external clock source is used, its frequency can be between 3 MHz and 24 MHz. The highest operating
frequency for the CPU and peripheral resource is 24 MHz. However, normal operation is not
guaranteed if a multiplication ratio resulting in a higher frequency than 24 MHz is specified.
Therefore, when 24 MHz external clock is inputted, 1 can be specified for the PLL clock multiplication
ratio. The PLL oscillation operates at the range of 4 MHz to 24 MHz, but the PLL oscillation range
differs by operation voltage and multiplication ratio. See the data sheet for the details.