UPD784938 Datasheet, PDF (106/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 4 CLOCK GENERATOR
Figure 4-2. Clock Oscillator External Circuitry
(a) Crystal/ceramic oscillation
µPD784938
VSS
X1
X2
(b) External clock
EXTC bit of OSTS = 1
µPD784938
X1
EXTC bit of OSTS = 0
µPD784938
X1
X2
µPD74HC04, etc.
Open
X2
Cautions 1. The oscillator should be as close as possible to the X1 and X2 pins.
2. No other signal lines should pass through the area enclosed by the dotted line.
Remark Differences between crystal resonator and ceramic resonator
Generally speaking, the oscillation frequency of a crystal resonator is extremely stable. It is therefore ideal for
performing high-precision time management (in clocks, frequency meters, etc.).
A ceramic resonator is inferior to a crystal resonator in terms of oscillation frequency stability, but it has three
advantages: a fast oscillation start-up time, small size, and low price. It is therefore suitable for general use (when
high-precision time management is not required). In addition, there are products with a built-in capacitor, etc.,
which enable the number of parts and mounting area to be reduced.
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Preliminary User’s Manual U13987EJ1V0UM00