Subsystem Clock Oscillator; External Circuit Of Subsystem Clock Oscillator; Examples Of Incorrect Oscillator Connection - NEC PD78052 User Manual

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
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 V
•
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
circuits is too long
IC
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.
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CHAPTER 7 CLOCK GENERATOR
IC
XT2
32.768
kHz
XT1
X2 X1
(b) External clock
XT2
External
XT1
Clock
PD74HCU04
(b) Signal lines intersect
each other
(n=0-7, 12, 13)
IC X2
. Do
SS
PORTn
X1