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EXTAL
V
CC
V
STBY
IH
EXTAL
φ (internal or
external)
RES
Figure 20.7 External Clock Output Settling Delay Timing
20.3
Duty Adjustment Circuit
When the oscillator frequency is 5 MHz or higher, the duty adjustment circuit adjusts the duty
cycle of the clock signal from the oscillator to generate φ.
20.4
Prescalers
The prescalers divide the system clock (φ) to generate internal clocks (φ/2 to φ/4096).
20.5
Frequency Divider
The frequency divider divides the duty-adjusted clock signal to generate the system clock (φ). The
frequency division ratio can be changed dynamically by modifying the value in DIVCR, as
described below. Power consumption in the chip is reduced in almost direct proportion to the
624
t
EXH
t
EXr
Figure 20.6 External Clock Input Timing
t
DEXT
t
EXL
× 0.7
V
CC
0.3 V
t
EXf
× 0.5
V
CC
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