EM78P342NP datasheet(77/102 Pages) EMC

77 / 102 page

EM78P341N/342N/343N

8-Bit Microprocessor with OTP ROM

Product Specification (V1.0) 12.01.2006

• 71

(This specification is subject to change without further notice)

Circuit diagrams for serial and parallel modes Crystal/Resonator

OSCI

7404

330

Crysta

7404

Fig. 6-19 Serial Mode Crystal/Resonator Circuit Diagram

OSCI

7404

10K

4.7K

Vdd

10K

Crystal

Fig. 6-20 Parallel Mode Crystal/Resonator Circuit Diagram

6.11.3 External RC Oscillator Mode

For some applications that do not require

precise timing calculation, the RC

oscillator (Fig. 6-21 at right) offers a cost-

effective solution. Nevertheless, it should

be noted that the frequency of the RC

oscillator is influenced by the supply

voltage, the values of the resistor (Rext),

the capacitor (Cext), and even by the

operation temperature. Moreover, the

frequency also changes slightly from one

chip to another due to manufacturing

process variations.

OSCI

Vcc

Rext

Cext

Fig. 6-21 External RC Oscillator Mode Circuit

In order to maintain a stable system frequency, the values of the Cext should be no less

than 20pF, and that of Rext should be no greater than 1M

Ω. If the frequency cannot be

kept within this range, the frequency can be affected easily by noise, humidity, and

leakage.

The smaller the Rext in the RC oscillator is, the faster its frequency will be. On the

contrary, for very low Rext values, for instance, 1 K

Ω, the oscillator will become

unstable because the NMOS cannot correctly discharge the capacitance current.

EM78P342NP Datasheet(PDF) 77 Page - ELAN Microelectronics Corp

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