ST7LITE20F2 datasheet(37/166 Pages) STMICROELECTRONICS

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ST7LITE20F2 ST7LITE25F2 ST7LITE29F2

Supply, reset and clock management

Doc ID 8349 Rev 5

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Note:

When the Multi-oscillator is not used, PB4 is selected by default as external clock.

Crystal/ceramic oscillators

This family of oscillators has the advantage of producing 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 Section 15.1: Option

bytes for more details on the frequency ranges). 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 startup 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 startup 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.

Table 7.

ST7 clock sources

Clock source

Hardware configuration

External clock

Crystal/ceramic resonators

Internal RC oscillator or

external clock on PB4

OSC1

OSC2

External

ST7

source

OSC1

OSC2

Load

capacitors

ST7

CL2

CL1

OSC1

OSC2

ST7

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