ST7L19 datasheet(21/138 Pages) STMICROELECTRONICS

21 / 138 page

ST7L15, ST7L19

21/138

7 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 re-

ducing the number of external components.

Main features

■ Clock Management

– 1 MHz internal RC oscillator (enabled by op-

tion byte

– 1 to 16 MHz External crystal/ceramic resona-

tor

– External Clock Input (enabled by option byte)

– PLL for multiplying the frequency by 8 or 4

(enabled by option byte). Only multiplying by 8

is available for ROM devices.

■ Reset Sequence Manager (RSM)

■ System Integrity Management (SI)

– main supply Low Voltage Detection (LVD)

with reset generation (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 (4.5V to 5.5V). It must be cali-

brated to obtain the frequency required in the ap-

plication. This is done by the software writing a 10-

bit calibration value in the RCCR (RC Control Reg-

ister) 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), that is, each time

the device is reset, the calibration value must be

loaded in the RCCR. Predefined calibration values

are stored in EEPROM for 3.3V and 5V VDD sup-

ply voltages at 25°C, as shown in the following ta-

ble.

Note:

1. DEE0h, DEE1h, DEE2h, and DEE3h addresses are lo-

cated in a reserved area but are special bytes containing

also the RC calibration values which are read-accessible

only in user mode. If all the EEPROM data or 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

four addresses.

For compatibility reasons with the SICSR register,

CR[1:0] bits are stored in the fifth and sixth position of the

DEE1 and DEE3 addresses.

Notes:

– In 38-pulse ICC mode, the internal RC oscillator

is forced as a clock source, regardless of the se-

lection in the option byte. For ST7L1 devices

which do not support the internal RC oscillator,

the “option byte disabled” mode must be used

(35-pulse ICC mode entry, clock provided by the

tool).

– For more information on the frequency and accu-

racy of the RC oscillator see “ELECTRICAL

CHARACTERISTICS” on page 98.

– To improve clock stability and frequency accura-

cy, it is recommended to place a decoupling ca-

pacitor, typically 100nF, between the VDD and

VSS pins as close as possible to the ST7 device.

– These bytes are systematically programmed by

ST, including on FASTROM devices.

Caution: If the voltage or temperature conditions

change in the application, the frequency may need

to be recalibrated.

Refer to application note AN1324 for information

on how to calibrate the RC frequency using an ex-

ternal reference signal.

RCCR

Conditions

ST7L1

Address

RCCRH0

VDD = 5V

TA = 25°C

fRC = 1 MHz

DEE0h1) (CR[9:2])

RCCRL0

DEE1h1) (CR[1:0])

RCCRH1

VDD = 3.3V

TA = 25°C

fRC = 1 MHz

DEE2h1) (CR[9:2])

RCCRL1

DEE3h1) (CR[1:0])

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