CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U16846EJ1V0UD
91
5.4 System Clock Oscillator
5.4.1 High-speed system clock oscillator
The following two high-speed system clock oscillators are available.
•
Crystal/ceramic oscillator: Oscillates a clock of f
XP
= 2 to 16 MHz
•
External RC oscillator:
Oscillates a clock of f
XP
= 3 to 4 MHz
High-speed system clock oscillation can be selected using the option byte. Refer to
CHAPTER 20 OPTION BYTE
for details.
(1) Crystal/ceramic oscillator
The crystal/ceramic oscillator oscillates with a crystal resonator or ceramic resonator (16 MHz (TYP.)) connected
to the X1 and X2 pins.
An external clock can be input to the crystal/ceramic oscillator. In this case, input the clock signal to the X1 pin
and input the inverse signal to the X2 pin.
Figure 5-9 shows the external circuit of the crystal/ceramic oscillator.
Figure 5-9. External Circuit of Crystal/Ceramic Oscillator
(a) Crystal, ceramic oscillation
(b) External clock
V
SS
X1
X2
Crystal resonator or
ceramic resonator
External
clock
X1
X2
Caution When using the crystal/ceramic oscillator, wire as follows in the area enclosed by the broken
lines in the Figure 5-9 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.
Figure 5-10 shows examples of incorrect resonator connection.
