System Clock Oscillators; Main System Clock Oscillator; External Circuit Of Main System Clock Oscillator - NEC PD789488 User Manual

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.
(a) Crystal or ceramic oscillation
Crystal
or
ceramic resonator
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
ground the capacitor to a ground pattern through which a high current flows.
• Do not fetch signals from the oscillator.
CHAPTER 5 CLOCK GENERATOR
Figure 5-7. External Circuit of Main System Clock Oscillator
V
SS
X1
X2
User's Manual U15331EJ4V1UD
(b) External clock
External
X1
clock
X2
. Do not
SS
101