AN977 Datasheet, PDF (11/17 Pages) STMicroelectronics – GUIDELINES FOR UPGRADING FROM THE ST92F120

GUIDELINES FOR UPGRADING FROM THE ST92F120 (0.50 µm) TO THE ST92F124...
Figure 3. ST92F120 Crystal Oscillator
CRYSTAL CLOCK
ST9
OSCIN
OSCOUT
Figure 4. ST92F150 Crystal Oscillator
CRYSTAL CLOCK
ST9
OSCIN
OSCOUT
C₁
C₂
1 MΩ *
*Recommended for oscillator stability
VR02116A
Rd*
C₁
C₂
*Rd can be inserted to reduce the drive level,
when using low drive crystals.
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 5. ST92F120 External Clock
Figure 6. ST92F150 External Clock
3.3 kΩ
INPUT
CLOCK
EXTERNAL CLOCK
OSCOUT
ST9
OSCIN
VR02116B
INPUT
CLOCK
EXTERNAL CLOCK
OSCIN
ST9
OSCOUT
VR02116B
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