ST7LITE20F2 datasheet(33/166 Pages) STMICROELECTRONICS

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ST7LITE20F2 ST7LITE25F2 ST7LITE29F2

Supply, reset and clock management

Doc ID 8349 Rev 5

33/166

Supply, reset and clock management

The device includes a range of utility features for securing the application in critical

situations (for example in case of a power brown-out), and reducing the number of external

components.

Main features

●

Clock management

–

1 MHz internal RC oscillator (enabled by option byte, available on ST7LITE25 and

ST7LITE29 devices only)

–

1 to 16 MHz or 32kHz External crystal/ceramic resonator (selected by option byte)

–

External Clock Input (enabled by option byte)

–

PLL for multiplying the frequency by 8 or 4 (enabled by option byte)

–

For clock ART counter only: PLL32 for multiplying the 8 MHz frequency by 4

(enabled by option byte). The 8 MHz input frequency is mandatory and can be

obtained in the following ways:

. 1 MHz RC + PLLx8

. 16 MHz external clock (internally divided by 2)

. 2 MHz external clock (internally divided by 2) + PLLx8

. Crystal oscillator with 16 MHz output frequency (internally divided by 2).

●

Reset Sequence Manager (RSM)

●

System Integrity Management (SI)

–

Main supply Low Voltage Detection (LVD) with reset generation (enabled by option

byte)

–

Auxiliary Voltage Detector (AVD) with interrupt capability for monitoring the main

supply (enabled by option byte).

7.1

Internal RC oscillator adjustment

The device contains an internal RC oscillator with an accuracy of 1% for a given device,

temperature and voltage range (4.5 V - 5.5 V). It must be calibrated to obtain the frequency

required in the application. This is done by software writing a calibration value in the RCCR

(RC Control Register).

Whenever the microcontroller is reset, the RCCR returns to its default value (FFh), i.e. each

time the device is reset, the calibration value must be loaded in the RCCR. Predefined

calibration values are stored in EEPROM for 3 and 5 V VDD supply voltages at 25 °C, as

shown in Table 6.

Table 6.

Predefined calibration values

RCCR

Conditions

ST7LITE29

address

ST7LITE25

address

RCCR0

VDD = 5 V, TA = 25 °C, fRC = 1 MHz

1000h and FFDEh

FFDEh

RCCR1

VDD = 3 V, TA = 25 °C, fRC = 700 kHz

1001h and FFDFh

FFDFh

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