ST72334J datasheet(33/125 Pages) STMICROELECTRONICS

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ST72334J/N, ST72314J/N, ST72124J

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4.4 SUPPLY, RESET AND CLOCK REGISTER DESCRIPTION

CLOCK RESET AND SUPPLY REGISTER

(CRSR)

Read/Write

Reset Value: 000x 000x (00h)

Bit 7:5 = Reserved, always read as 0.

Bit 4 = LVDRF

LVD reset flag

This bit indicates that the last Reset was generat-

ed by the LVD block. It is set by hardware (LVD re-

set) and cleared by software (writing zero). See

WDGRF flag description for more details. When

the LVD is disabled by OPTION BYTE, the LVDRF

bit value is undefined.

Bit 3 = Reserved, always read as 0.

Bit 2 = CSSIE

Clock security syst

interrupt enable

This bit enables the interrupt when a disturbance

is detected by the Clock Security System (CSSD

bit set). It is set and cleared by software.

0: Clock security system interrupt disabled

1: Clock security system interrupt enabled

When the CSS is disabled by OPTION BYTE, the

CSSIE bit has no effect.

Bit 1 = CSSD

Clock security system detection

This bit indicates that the safe oscillator of the

Clock Security System block has been selected by

hardware due to a disturbance on the main clock

signal (fOSC). It is set by hardware and cleared by

a read of the CRSR register when the original os-

cillator recovers.

0: Safe oscillator is not active

1: Safe oscillator has been activated

When the CSS is disabled by OPTION BYTE, the

CSSD bit value is forced to 0.

Bit 0 = WDGRF

Watchdog reset flag

This bit indicates that the last Reset was generat-

ed by the Watchdog peripheral. It is set by hard-

ware (watchdog reset) and cleared by software

(writing zero) or a LVD Reset (to ensure a stable

cleared state of the WDGRF flag when CPU

starts).

Combined with the LVDRF flag information, the

flag description is given by the following table.

Application notes

In case the LVDRF flag is not cleared upon anoth-

er RESET type occurs (extern or watchdog), the

LVDRF flag remains set to keep trace of the origi-

nal failure.

In this condition, a watchdog reset can be detect-

ed by the software while an external reset not.

Table 4. Clock, Reset and Supply Register Map and Reset Values

LVD

CSS

WDG

RESET Sources

LVDRF

WDGRF

External RESET pin

Watchdog

LVD

Address

(Hex.)

Label

765

321

002Bh

CRSR

Reset Value

LVDRF

CFIE

CSSD

WDGRF

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