ELANSC310 datasheet(85/119 Pages) AMD

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Élan™SC310 Microcontroller Data Sheet

PREL IMINARY

frequency. It is therefore required that the load capaci-

tance in the oscillator circuit is duplicated as closely as

possible to the manufacturer’s load capacitance speci-

fication.

The crystal load capacitance in the circuit consists of

the capacitor network C

O, CSTRAY, CD, and CG. This net-

work reduces to (C

O + CSTRAY) in parallel with the series

combination of C

D and CG. Therefore, the desired se-

ries combination of C

D and CG is equal to CL – (CO +

CSTRAY), where CL is the crystal manufacturer’s load ca-

pacitance specification.

STRAY is typically difficult to determine. Some value

can be assumed and experimentation will determine

the optimal value for CD and CG. In determining the ex-

ternal component values to provide the optimal operat-

ing frequency, there are some recommended limits to

ensure a reasonable start-up time for the oscillator cir-

cuit. These limits are shown in Table 43.

The series combination of CD and CG =

(

×)

G )

(

---------------------------







Table 43.

Recommended Oscillator Component

Value Limits

Minimum

Maximum

14 M

Ω

18 M

Ω

10 k

Ω

10 pF

30 pF

10 pF

30 pF

ÉlanSC310 Microcontroller

X32IN (201)

X32OUT (202)

XTAL

CSTRAY

Notes:

For board layout suggestions, refer to the ÉlanSC310 Microcontroller Evaluation Board User’s Manual available in PDF format

on the AMD web site.

Figure 29.

X32 Oscillator Circuit

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