NEC PD78F9488 - Manual (Page 101)

CHAPTER 5 CLOCK GENERATOR
User’s Manual U15331EJ4V1UD
101
5.4 System Clock Oscillators
5.4.1 Main system clock oscillator
The main 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 5-7 shows the external circuit of the main system clock oscillator.
Figure 5-7. External Circuit of Main System Clock Oscillator
(a) Crystal or ceramic oscillation (b) External clock
Crystal
or
ceramic resonator
V SS
X2
X1
External
clock
X1
X2
Caution When using the main system clock oscillator, wire as follows in the area enclosed by the broken
lines in Figure 5-7 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.