ST7LITEUS5 datasheet(28/136 Pages) STMICROELECTRONICS

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Supply, reset and clock management

ST7LITEUS2, ST7LITEUS5

28/136

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.

6.1

Main features

●

Clock management

–

8 MHz internal RC oscillator (enabled by option byte)

–

External clock Input (enabled by option byte)

●

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

6.2

Internal RC oscillator adjustment

The ST7 contains an internal RC oscillator with a specific accuracy for a given device,

temperature and voltage. It can be selected as the start up clock through the CKSEL[1:0]

option bits (see Section 14.1 on page 123). 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 Flash memory for 3.3 and 5 V VDD supply voltages at 25°C,

as shown in the following table.

Table 5.

Predefined RC oscillator calibration values

RCCR

Conditions

ST7LITEUS2/ST7LITEUS5 address

RCCRH0

VDD=5 V

TA=25 °C

fRC=8 MHz

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

DEE0h, DEE1h, DEE2h and DEE3h are located in a reserved area butare special bytes containing also

the RC calibration values which are read-accessible only in user mode. If all the Flash space (including the

RC calibration value locations) has been erased (after the readout protection removal), then the RC

calibration values can still be obtained through these two addresses.

RCCRL0

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

RCCRH1

VDD=3.3 V

TA=25 °C

fRC=8 MHz

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

RCCRL1

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

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