ST7LITE49K2 datasheet(42/245 Pages) STMICROELECTRONICS

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Supply, reset and clock management

ST7LITE49K2

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7.2

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 16 MHz):

●

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 6. Refer to the electrical characteristics section for more details.

7.2.1

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 OSCI1 and OSCI2 must be tied to ground, and PB1 is

selected by default as the external clock.

7.2.2

Crystal/ceramic oscillators

In this mode, with a self-controlled gain feature, oscillator of any frequency from 1 to 16 MHz

can be placed on OSC1 and OSC2 pins. This family of oscillators has the advantage of

producing a very accurate 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 possible to

the oscillator pins in order to minimize output distortion and start-up stabilization time. The

loading capacitance 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.

7.2.3

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.

The calibration is done through the RCCR[7:0] and SICSR[6:5] registers.

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