Hardware manual

Rev. 3.0, 09/98, page 80 of 361
(2) Input of External Clock Signal
①① Circuit Configuration: An external clock signal can be input as shown in the examples in
figure 5.5. In example (b) in figure 5.5, the external clock signal should be kept high during
standby.
EXTAL
XTAL
External clock input
74HC04
(b)
EXTAL
XTAL
External clock input
Open
(a)
Figure 5.5 External Clock Input (Example)
②② External Clock Input
Frequency Double the system clock (φ) frequency
Duty factor 45% to 55%
5.3 System Clock Divider
The system clock divider divides the crystal oscillator or external clock frequency by 2 to create
the system clock (φ).