System Clock Oscillators; High-Speed Internal Oscillator; Crystal/Ceramic Oscillator - NEC 78K0S/KU1+ User Manual

5.4

System Clock Oscillators

The following three types of system clock oscillators are available.

• High-speed internal oscillator:

• Crystal/ceramic oscillator:

• External clock input circuit:
5.4.1 High-speed internal oscillator
The 78K0S/KU1+ include a high-speed internal oscillator (8 MHz (TYP.)).
If the high-speed internal oscillation is selected by the option byte as the clock source, the X1 and X2 pins can be
used as I/O port pins.
For details of the option byte, refer to CHAPTER 15 OPTION BYTE. For details of I/O ports, refer to CHAPTER 4
PORT FUNCTIONS.
5.4.2 Crystal/ceramic oscillator
The crystal/ceramic oscillator oscillates using a crystal or ceramic resonator connected between the X1 and X2
pins.
If the crystal/ceramic oscillator is selected by the option byte as the system clock source, the X1 and X2 pins are
used as crystal or ceramic resonator connection pins.
For details of the option byte, refer to CHAPTER 15 OPTION BYTE. For details of I/O ports, refer to CHAPTER 4
PORT FUNCTIONS.
Figure 5-6 shows the external circuit of the crystal/ceramic oscillator.
Caution When using the crystal/ceramic oscillator, wire as follows in the area enclosed by the broken
lines in Figure 5-6 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.
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CHAPTER 5 CLOCK GENERATORS
Internally oscillates a clock of 8 MHz (TYP.).
Oscillates a clock of 2 MHz to 10 MHz.
Supplies a clock of 2 MHz to 10 MHz to the X1 pin.
Figure 5-6. External Circuit of Crystal/Ceramic Oscillator
Crystal resonator
or ceramic resonator
User's Manual U18172EJ2V0UD
V
SS
X1
X2
. Do not
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