ST72F264G ST Microelectronics, ST72F264G Datasheet - Page 21

• Manufacturer Part Number: ST72F264G
• Description: (ST72F260G - ST72F264G) 8-BIT MCU
• Manufacturer: ST Microelectronics

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DataSheet
6.2 MULTI-OSCILLATOR (MO)
The main clock of the ST7 can be generated by
four different source types coming from the multi-
oscillator block:
Each oscillator is optimized for a given frequency
range in terms of consumption and is selectable
through the option byte. The associated hardware
configurations are shown in
electrical characteristics section for more details.
Caution: The OSC1 and/or OSC2 pins must not
be left unconnected. For the purposes of Failure
Mode and Effects Analysis, it should be noted that
if the OSC1 and/or OSC2 pins are left unconnect-
ed, the ST7 main oscillator may start and, in this
configuration, could generate an f
quency in excess of the allowed maximum
(>16MHz.), putting the ST7 in an unsafe/unde-
fined state. The product behaviour must therefore
be considered undefined when the OSC pins are
left unconnected.
External Clock Source
In this external clock mode, a clock signal (square,
sinus or triangle) with ~50% duty cycle has to drive
the OSC1 pin while the OSC2 pin is tied to ground.
Crystal/Ceramic Oscillators
This family of oscillators has the advantage of pro-
ducing a very accurate rate on the main clock of
the ST7. The selection within a list of 5 oscillators
with different frequency ranges has to be done by
option byte in order to reduce consumption (refer
to
the frequency ranges). In this mode of the multi-
oscillator, the resonator and the load capacitors
have to be placed as close as possible to the oscil-
lator pins in order to minimize output distortion and
start-up stabilization time. The loading capaci-
tance values must be adjusted according to the
selected oscillator.
These oscillators are not stopped during the
RESET phase to avoid losing time in the oscillator
start-up phase.
an external source
5 crystal or ceramic resonator oscillators
an internal high frequency RC oscillator
Section 15.1 on page 157
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Table
for more details on
3. Refer to the
OSC
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clock fre-
Internal RC Oscillator
This oscillator allows a low cost solution for the
main clock of the ST7 using only an internal resis-
tor and capacitor. Internal RC oscillator mode has
the drawback of a lower frequency accuracy and
should not be used in applications that require ac-
curate timing.
In this mode, the two oscillator pins have to be tied
to ground.
Table 3. ST7 Clock Sources
ST72260G, ST72262G, ST72264G
C
L1
Hardware Configuration
EXTERNAL
SOURCE
OSC1
OSC1
OSC1
CAPACITORS
LOAD
ST7
ST7
ST7
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OSC2
OSC2
OSC2
C
L2
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