COP8-REF-AM datasheet(21/83 Pages) NSC

21 / 83 page

10.0 Functional Description (Continued)

10.8 OSCILLATOR CIRCUITS

The device has two crystal oscillators to facilitate low power

operation while maintaining throughput when required. Fur-

ther information on the use of the two oscillators is found in

Section 7.0 Power Saving Features. The low speed oscillator

utilizes the L0 and L1 port pins. References in the following

text to CKI will also apply to L0 and references to G7/CKO

will also apply to L1.

10.8.1 Oscillator

CKI is the clock input while G7/CKO is the clock generator

output to the crystal. An on-chip bias resistor connected

between CKI and CKO is provided to reduce system part

count. The value of the resistor is in the range of 0.5M to 2M

(typically 1.0M). Table 2 shows the component values re-

quired for various standard crystal values. Resistor R2 is

on-chip, for the high speed oscillator, and is shown for

reference. Figure 11 shows the crystal oscillator connection

diagram. A ceramic resonator of the required frequency may

be used in place of a crystal if the accuracy requirements are

not quite as strict.

TABLE 2. Crystal Oscillator Configuration,

A = 25˚C, VCC =5V

R1 (k

Ω)R2 (MΩ)

C1 (pF)

C2 (pF)

CKI Freq.

(MHz)

On Chip

18–36

5.6

On Chip

100

100–156

0.455

32.768

kHz*

*Applies to connection to low speed oscillator on port pins L0 and L1 only.

**See Note below.

20006313

FIGURE 9. Brownout Reset Operation

20006314

FIGURE 10. Reset Circuit Using Power-On Reset

COP8-REF-AM 数据表(PDF) 21 Page - National Semiconductor (TI)

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