ST72511R datasheet(27/164 Pages) STMICROELECTRONICS

27 / 164 page

ST72311R, ST72511R, ST72512R, ST72532R

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5.3 LOW CONSUMPTION OSCILLATOR

The fOSC main clock of the ST7 can be generated

by two different source types:

an external source

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 Configur ation

OSC1

OSC2

EXTERNAL

ST7

SOURCE

VDD

ROBP

OSC1

OSC2

LOAD

CAPACITORS

ST7

CL2

CL1

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