ST7FOXK2 datasheet(34/226 Pages) STMICROELECTRONICS

34 / 226 page

Supply, reset and clock management

ST7FOXF1, ST7FOXK1, ST7FOXK2

34/226

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)

●

Reset Sequence Manager (RSM)

●

System Integrity management (SI)

–

Main supply Low voltage detection (LVD) with reset generation (enabled by option

byte)

6.1

RC oscillator adjustment

6.1.1

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

RCCRH (RC Control register High) and in the bits 6:5 in the RCCRL (RC Control register

Low).

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 for 5 V VDD supply voltage at 25 °C (see Table 7).

In 38-pulse ICC mode, the internal RC oscillator is forced as a clock source, regardless of

the selection in the option byte.

Section 12: Electrical characteristics on page 187 for more information on the frequency

and accuracy of the RC oscillator.

To improve clock stability and frequency accuracy, it is recommended to place a decoupling

capacitor, typically 100 nF, between the VDD and VSS pins and also between the VDDA and

VSSA pins as close as possible to the ST7 device.

Table 7.

Predefined RC oscillator calibration values

RCCR

Conditions

ST7FOX

Address

RCCRH

VDD= 5V

TA= 25°C

fRC = 8 MHz

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

The DEE0h and DEE1h addresses are located in a reserved area in non-volatile memory. They are read-

only bytes for the application code. This area cannot be erased or programmed by any ICC operations.

For compatibility reasons with the RCCRL register, CR[1:0] bits are stored in the 5th and 6th position of

DEE1 address.

RCCRL

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

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