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GUIDELINES FOR UPGRADING FROM THE ST92F120 (0.50 µm) TO THE ST92F124...

2.4.1.2 Leakages

While the ST92F120 is sensitive to leakage from GND to OSCIN, the ST92F124/F1 50/F250

is sensitive to leakage from VDD to OSCIN. It is recommended to surround the crystal oscil-

lator by a ground ring on the printed circuit board and to apply a coating film to avoid humidity

problems, if necessary.

2.4.1.3 External clock

Even if compatibility with the ST92F120 board design is maintained, it is recommended to

apply the external clock on the OSCOUT input.

The advantages are:

– a standard TTL input signal can be used whereas the ST92F120 Vil on the external clock is

between 400mV and 500mV.

– the external resistor between OSCOUT and VDD is not required.

Figure 3. ST92F120 Crystal Oscillator

Figure 4. ST92F150 Crystal Oscillator

OSCIN

OSCOUT

ST9

CRYSTAL CLOCK

VR02116A

1 M

Ω *

*Recommended for oscillator stability

OSCIN

OSCOUT

ST9

CRYSTAL CLOCK

*Rd can be inserted to reduce the drive level,

Rd*

Figure 5. ST92F120 External Clock

Figure 6. ST92F150 External Clock

OSCIN

OSCOUT

CLOCK

INPUT

EXTERNAL CLOCK

VR02116B

ST9

3.3 k

Ω

OSCOUT

OSCIN

CLOCK

INPUT

EXTERNAL CLOCK

VR02116B

ST9