Notes; Inputting An External Clock; Using The Crystal/Ceramic Oscillator; Point From Which Signals Can Be Drawn When An External Clock Is Input - NEC PD78212 User Manual

8-bit single-chip microcomputer sub-series
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µ PD78214 Sub-Series
Remark Different uses of the crystal and ceramic resonator
Generally, a crystal's oscillation frequency is quite stable. Crystals are ideal for high-precision time management (for example, clock
or frequency measurement). In comparison with crystals, ceramic resonators are less stable but offer three advantages: a shorter
oscillation start time, smaller dimensions, and lower price. Ceramic resonators are suitable for general applications (which do not
require high-precision time management). If a ceramic resonator incorporating capacitors is used, the number of components and
the mounting area can be reduced.

4.2 NOTES

Regarding the clock generator, note the following:

4.2.1 Inputting an External Clock

(1) When inputting an external clock, do not select STOP mode. The clock generator may be damaged. At least,
its reliability will be adversely affected.
(2) When inputting an external clock, input the clock signal to pin X1 and the inverted signal to pin X2. If the
inverted signal is not input to the pin X2, malfunctions may readily occur due to noise.
(3) When inputting an external clock, use HCMOS or a device having equivalent drive capability.
(4) Do not draw signals from pins X1 and X2. Draw signals from point a shown in Fig. 4-3.
Fig. 4-3 Point from Which Signals Can Be Drawn When an External Clock Is Input
(5) Minimize the length of the line connecting pin X1 to pin X2 through the inverter.

4.2.2 Using the Crystal/Ceramic Oscillator

(1) The oscillator is a high-frequency analog circuit. Use the oscillator carefully. Special notes are given below:
• Minimize the lengths of the wiring.
• Do not let other signal lines cross this circuit.
• Keep the oscillator away from a line through which a varying high current flows.
• Always ground the capacitors of the oscillator at the same potential as pin V
capacitors to a ground pattern through which a high current flows.
• Do not draw signals from the oscillator.
The microcomputer is capable of normal, stable operation only when the oscillation is normal and stable. If
a high-precision oscillation frequency is required, consult with the oscillator manufacturer.
56
µ
a
X1
X2
PD78214
. Do not ground the
SS

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