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CHAPTER 6 CLOCK GENERATOR
6.4 System Clock Oscillator
6.4.1 Main system clock oscillator
The main system clock oscillator oscillates with a crystal resonator or a ceramic resonator (standard: 8.38 MHz)
connected to the X1 and X2 pins.
External clocks can be input to the main system clock oscillator. In this case, input a clock signal to the X1 pin
and an inverted clock signal to the X2 pin.
Figure 6-4 shows an external circuit of the main system clock oscillator.
Figure 6-4. External Circuit of Main System Clock Oscillator
(a) Crystal and ceramic oscillation
(b) External clock
Crystal resonator or
ceramic resonator
X2
X1
PD74HCU04
External
clock
X2
X1
IC
µ
Caution
Do not execute the STOP instruction while an external clock is input. This is because if the STOP
instruction is executed, the main system clock operation is stopped, and the X2 pin is connected
to V
DD
, via a pull-up resistor.
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