ST72325 STMICROELECTRONICS [STMicroelectronics], ST72325 Datasheet - Page 28

• Manufacturer Part Number: ST72325
• Description: 8-BIT MCU WITH 16 TO 60K FLASH/ROM, ADC, CSS, FIVE TIMERS, SPI, SCI, I2C INTERFACE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST72325
6.2 MULTI-OSCILLATOR (MO)
The main clock of the ST7 can be generated by
three 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.
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 4 oscillators
with different frequency ranges has to be done by
option byte in order to reduce consumption (refer
to
frequency ranges). In this mode of the multi-oscil-
lator, the resonator and the load capacitors have
to be placed as close as possible to the oscillator
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.
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
28/193
section 14.1 on page 179
an external source
4 crystal or ceramic resonator oscillators
an internal high frequency RC oscillator
for more details on the
Table
5. Refer to the
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 5. ST7 Clock Sources
C
L1
EXTERNAL
Hardware Configuration
SOURCE
OSC1
OSC1
OSC1
CAPACITORS
LOAD
ST7
ST7
ST7
OSC2
OSC2
OSC2
C
L2