CHAPTER 7 CLOCK GENERATOR (
µ
PD789860 SUBSERIES)
User’s Manual U14826EJ5V0UD
71
7.4 System Clock Oscillators
7.4.1 System clock oscillator
The system clock oscillator is oscillated by the crystal or ceramic resonator (5.0 MHz TYP.) connected across the
X1 and X2 pins.
An external clock can also be input to the circuit. In this case, input the clock signal to the X1 pin, and input the
inverted signal to the X2 pin.
Figure 7-3 shows the external circuit of the system clock oscillator.
Figure 7-3. External Circuit of System Clock Oscillator
(a) Crystal or ceramic oscillation
(b) External clock
V
SS
X1
X2
Crystal
or
ceramic resonator
External
clock
X1
X2
Caution When using the system clock oscillator, wire as follows in the area enclosed by the broken lines
in Figure 7-3 to avoid an adverse effect from wiring capacitance.
•
Keep the wiring length as short as possible.
•
Do not cross the wiring with the other signal lines. Do not route the wiring near a signal line
through which a high fluctuating current flows.
•
Always make the ground point of the oscillator capacitor the same potential as V
SS
. Do not
ground the capacitor to a ground pattern through which a high current flows.
•
Do not fetch signals from the oscillator.