EM78P447SAM datasheet(25/55 Pages) EMC

25 / 55 page

EM78P447S

OTP ROM

OSCI

OSCO

EM 78P447S

Ext. Clock

Fig. 10 Crystal/Resonator Circuit

OSCI

OSCO

EM 78P447S

XTAL

Fig. 11 Crystal/Resonator Circuit

Table 10 Capacitor Selection Guide for Crystal Oscillator or Ceramic Resonator

Oscillator Type

Frequency Mode

Frequency

C1(pF)

C2(pF)

455 kHz

100~150

2.0 MHz

20~40

Ceramic Resonators

HXT

4.0 MHz

10~30

32.768kHz

100KHz

LXT

200KHz

455KHz

20~40

20~150

1.0MHz

15~30

2.0MHz

Crystal Oscillator

HXT

4.0MHz

For some applications that do not need a very precise timing calculation, the RC oscillator (Fig. 15) offers a lot of cost

savings. 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 the manufacturing process variation.

In order to maintain a stable system frequency, the values of the Cext should not be less than 20pF, and that the value

of Rext should not be greater than 1 M ohm. If they cannot be kept in this range, the frequency is easily affected by noise,

This specification is subject to change without prior notice.

06.25.2003 (V1.1)

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