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CHAPTER 4 CLOCKS
MB90620 series
4.1
Clocks
The clock generator controls the operation of the internal clock for the CPU and
peripheral functions. This internal clock is called the machine clock. One internal clock
cycle is regarded as one machine cycle.
Other clocks include a clock generated by source oscillation, called an oscillation
clock, and a clock generated by the internal PLL oscillation, called a PLL clock.
I
Clocks
The clock generator block contains the oscillation circuit that generates the oscillation clock. An
external oscillator is connected to this circuit. The oscillation clock can also be supplied by
inputting an external clock to the clock generator.
The clock generator also contains the PLL clock multiplier circuit, which generates four types of
clock, that are multiples of the oscillation clock.
The clock generator controls the oscillation stabilization wait interval and PLL clock multiplication
as well as controls internal clock operation by changing the clock with a clock selector.
G
Oscillation clock (HCLK)
The oscillation clock is generated either from an external oscillator connected to the oscillation
circuit or by input of an external clock.
G
Main clock (MCLK)
The main clock, which is the oscillation clock divided by 2, supplies the clock input to the
timebase timer and the clock selector.
G
PLL clock (PCLK)
The PLL clock is obtained by multiplying the oscillation clock with the internal PLL clock
multiplier circuit (PLL oscillation circuit). Selection can be made from among four different PLL
clocks.
G
Machine clock (
φ
)
The machine clock controls operation of the operation of the CPU and peripheral functions. One
clock cycle is regarded as one machine cycle (1/
φ
). An operating machine clock can be selected
from among the main clock that is generated from the oscillation clock divided by 2 and the four
types of clock, that are multiples of the source clock frequency.
<Check>
Although an oscillation clock of 3 MHz to 32 MHz can be generated when the operating
voltage is 5 V, the maximum operating frequency for the CPU and peripheral functions is
16 MHz. If a frequency multiplier rate exceeding the operating frequency is specified, devices
will not operate correctly.
If, for example, a source oscillation of 16 MHz is generated, only a multiplier of 1 can be
specified.
<Reference>
A PLL oscillation of 3 to 16 MHz is possible, but this range depends on the operating voltage
and multiplier. See "Data Sheet," for details.