UPD78F9234MC-5A4-A Datasheet, PDF (80/419 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

CHAPTER 5 CLOCK GENERATORS
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:
Internally oscillates a clock of 8 MHz (TYP.).
Oscillates a clock of 2 to 10 MHz.
Supplies a clock of 2 to 10 MHz to the X1 pin.
5.4.1 High-speed internal oscillator
The 78K0S/KB1+ includes 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 18 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 18 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.
Figure 5-6. External Circuit of Crystal/Ceramic Oscillator
VSS
X1
X2
Crystal resonator
or ceramic resonator
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 VSS. Do not
ground the capacitor to a ground pattern through which a high current flows.
• Do not fetch signals from the oscillator.
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User’s Manual U17446EJ5V0UD