ST72311R, ST72511R, ST72512R, ST72532R
5.3 LOW CONSUMPTION OSCILLATOR
The fOSC main clock of the ST7 can be generated
by two different source types:
s an external source
s a crystal or ceramic resonator oscillators
The associated hardware configuration are shown
in Table 4. Refer to the 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 Oscillator
This oscillator (based on constant current source)
is optimized in terms of consumption and has the
advantage of producing a very accurate rate on
the main clock of the ST7.
When using this oscillator, the resonator and the
load capacitances have to be connected as shown
in Table 4 and have to be mounted as close as
possible to the oscillator pins in order to minimize
output distortion and start-up stabilization time.
This oscillator is not stopped during the RESET
phase to avoid losing time in the oscillator start-up
phase.
These oscillators are not stopped during the
RESET phase to avoid losing time in the oscillator
start-up phase.
Table 4. ST7 Clock Sources
Hardware Configuration
ST7
VDD
OSC1
OSC2
EXTERNAL
SOURCE
ROBP
ST7
OSC1
OSC2
CL1
CL2
LOAD
CAPACITORS
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