Subsystem Clock Oscillator; External Circuit Of Subsystem Clock Oscillator - NEC mPD780208 Subseries User Manual

8-bit single-chip microcontrollers
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5.4.2 Subsystem clock oscillator

The subsystem clock oscillator oscillates with a crystal resonator (standard: 32.768 kHz) connected to the XT1
and XT2 pins.
External clocks can be input to the subsystem clock oscillator. In this case, input a clock signal to the XT1 pin
and its inverted signal to the XT2 pin.
Figure 5-7 shows an external circuit of the subsystem clock oscillator.
Figure 5-7. External Circuit of Subsystem Clock Oscillator
(a) Crystal oscillation
32.768
Cautions 1. When using the main system or subsystem clock oscillator, wire as follows in the area
enclosed by the broken lines in Figures 5-6 and 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
not ground the capacitor to a ground pattern through which a high current flows.
• Do not fetch signals from the oscillator.
When using the subsystem clock oscillator, pay special attention because the subsystem
clock oscillator has low amplification to minimize power consumption.
Figure 5-8 shows examples of incorrect resonator connection.
110
CHAPTER 5 CLOCK GENERATOR
External
XT1
kHz
XT2
IC
User's Manual U11302EJ4V0UM
(b) External clock
XT1
clock
XT2
. Do
SS

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