Datasheet

78K0/Ix2 CHAPTER 5 CLOCK GENERATOR
R01UH0010EJ0500 Rev.5.00 166
Feb 28, 2012
5.4 System Clock Oscillator
5.4.1 X1 oscillator
T
he X1 oscillator oscillates with a crystal resonator or ceramic resonator (clock-through mode: 1 to 10 MHz, PLL mode:
4 MHz) connected to the X1 and X2 pins.
An external clock can also be input. In this case, input the clock signal (clock-through mode: 1 to 10 MHz, PLL mode: 4
MHz) to the EXCLK pin.
Figure 5-9 shows an example of the external circuit of the X1 oscillator.
Figure 5-9. Example of External Circuit of X1 Oscillator
(a) Crystal or ceramic oscillation (b) External clock
X1
X2
V
SS
EXCLK
External clock
Cautions are listed on the next page.
Caution. When using the X1 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.
Figure 5-10. Examples of Incorrect Resonator Connection (1/2)
(a) Too long wiring (b) Crossed signal line
X2V SS X1 X1V SS X2
PORT