ST7LITE1XB datasheet(27/157 Pages) STMICROELECTRONICS

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ST7LITE1xB

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7.4 MULTI-OSCILLATOR (MO)

The main clock of the ST7 can be generated by

four different source types coming from the multi-

oscillator block (1 to 16MHz):

■ an external source

■ 5 different configurations for crystal or ceramic

resonator oscillators

■ an internal high frequency RC oscillator

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 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.

Note: when the Multi-Oscillator is not used, PB4 is

selected by default as external clock.

Crystal/Ceramic Oscillators

In this mode, with a self-controlled gain feature,

oscillator of any frequency from 1 to 16MHz can be

placed on OSC1 and OSC2 pins. This family of os-

cillators has the advantage of producing a very ac-

curate rate on the main clock of the ST7. In this

mode of the multi-oscillator, the resonator and the

load capacitors have to be placed as close as pos-

sible to the oscillator pins in order to minimize out-

put distortion and start-up stabilization time. The

loading capacitance values must be adjusted ac-

cording 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

In this mode, the tunable 1%RC oscillator is used

as main clock source. The two oscillator pins have

to be tied to ground if dedicately using for oscillator

else can be found as general purpose IO.

The calibration is done through the RCCR[7:0] and

SICSR[6:5] registers.

Table 4. ST7 Clock Sources

Hardware Configuration

OSC1

OSC2

EXTERNAL

ST7

SOURCE

OSC1

OSC2

LOAD

CAPACITORS

ST7

CL2

CL1

OSC1

OSC2

ST7

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