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CHAPTER 7 CLOCK GENERATOR
IC X2 X1
7.4.2 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 main system clock oscillator. In this case, input a clock signal to the XT1 pin
and an antiphase clock signal to the XT2 pin.
Figure 7-7 shows an external circuit of the subsystem clock oscillator.
Figure 7-7. External Circuit of Subsystem Clock Oscillator
(a) Crystal oscillation (b) External clock
Remark When using a subsystem clock, replace X1 and X2 with XT1 and XT2, respectively. Further, insert
resistors in series on the side of XT2.
X2 X1
PORTn
(n=0-7, 12, 13)
IC
External
Clock
XT2
XT1
PD74HCU04
µ
XT2
XT1
32.768
kHz
IC
Cautions 1. When using a main system clock oscillator and a subsystem clock oscillator, carry out wiring
in the broken line area in Figures 7-6 and 7-7 to prevent any effects from wiring capacities.
•Minimize the wiring length.
•Do not allow wiring to intersect with other signal conductors. Do not allow wiring to come
near changing high current.
•Set the potential of the grounding position of the oscillator capacitor to that of VSS. Do
not ground to any ground pattern where high current is present.
•Do not fetch signals from the oscillator.
Take special note of the fact that the subsystem clock oscillator is a circuit with low-level
amplification so that current consumption is maintained at low levels.
Figure 7-8 shows examples of incorrect oscillator connection.
Figure 7-8. Examples of Incorrect Oscillator Connection (1/2)
(a) Wiring of connection (b) Signal lines intersect
circuits is too long each other