ST7LITE49K2 datasheet(38/245 Pages) STMICROELECTRONICS

38 / 245 page

Supply, reset and clock management

ST7LITE49K2

38/245

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. The main features are the following:

●

Clock management

–

8 MHz internal RC oscillator (enabled by option byte)

–

Auto-wakeup RC oscillator (enabled by option byte)

–

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

–

External clock input (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:

- from 8-MHz internal RC oscillator

- from 16-MHz external crystal/ceramic resonator (divided internally by two by

default)

●

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

RC oscillator adjustment

7.1.1

Internal RC oscillator

The device contains an internal RC oscillator with a specific accuracy 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 10-bit calibration value in the

RCCR (RC Control register) and in the bits 6:5 in the SICSR (SI Control Status 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 (see

Table 5).

Table 5.

Predefined RC oscillator calibration values

RCCR

Conditions

ST7LITE49K2

Address

RCCRH0

VDD= 5V

TA= 25°C

fRC = 8 MHz

DEE0h(1) (CR[9:2])

RCCRL0

DEE1h(1) (CR[1:0])

RCCRH1

VDD = 3.3 V

TA= 25°C

fRC = 8 MHz

DEE2h(1) (CR[9:2])

RCCRL1

DEE3h(1) (CR[1:0])

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