ST7LITE09 datasheet(30/122 Pages) STMICROELECTRONICS

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ST7LITE0, ST7SUPERLITE

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SYSTEM INTEGRITY MANAGEMENT (Cont’d)

7.5.2 Auxiliary Voltage Detector (AVD)

The Voltage Detector function (AVD) is based on

an analog comparison between a VIT-(AVD) and

VIT+(AVD) reference value and the VDD main sup-

ply voltage (VAVD). The VIT-(AVD) reference value

for falling voltage is lower than the VIT+(AVD) refer-

ence value for rising voltage in order to avoid par-

asitic detection (hysteresis).

The output of the AVD comparator is directly read-

able by the application software through a real

time status bit (AVDF) in the SICSR register. This

bit is read only.

Caution: The AVD functions only if the LVD is en-

abled through the option byte.

7.5.2.1 Monitoring the VDD Main Supply

The AVD voltage threshold value is relative to the

selected LVD threshold configured by option byte

(see section 15.1 on page 109).

If the AVD interrupt is enabled, an interrupt is gen-

erated when the voltage crosses the VIT+(LVD) or

VIT-(AVD) threshold (AVDF bit is set).

In the case of a drop in voltage, the AVD interrupt

acts as an early warning, allowing software to shut

down safely before the LVD resets the microcon-

troller. See Figure 19.

The interrupt on the rising edge is used to inform

the application that the VDD warning state is over

Figure 19. Using the AVD to Monitor VDD

VDD

VIT+(AVD)

VIT-(AVD)

AVDF bit

RESET

IF AVDIE bit = 1

Vhyst

AVD INTERRUPT

REQUEST

INTERRUPT Cleared by

VIT+(LVD)

VIT-(LVD)

LVD RESET

Early Warning Interrupt

(Power has dropped, MCU not

not yet in reset)

hardware

INTERRUPT Cleared by

reset

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