System Clock Oscillators; System Clock Oscillator - NEC PD789860 User Manual

8.4 System Clock Oscillators

8.4.1 System clock oscillator

The system clock oscillator is oscillated by the resistor (R) and capacitor (C) (1.0 MHz TYP.) connected across the
CL1 and CL2 pins.
An external clock can also be input to the circuit. In this case, input the clock signal to the CL1 pin, and input the
inverted signal to the CL2 pin.
Figure 8-3 shows the external circuit of the system clock oscillator.
(a) RC oscillation
C
Caution When using the system clock oscillator, wire as follows in the area enclosed by the broken lines
in Figure 8-3 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.
78
CHAPTER 8 CLOCK GENERATOR (
Figure 8-3. External Circuit of System Clock Oscillator
CL1
R
CL2
V
SS
User's Manual U14826EJ5V0UD
µ
PD789861 SUBSERIES)
(b) External clock
External
clock
CL1
CL2
. Do not
SS