ST7LITEUS5 datasheet(45/136 Pages) STMICROELECTRONICS

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Interrupts

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7.4.2

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 supply voltage (VAVD). The VIT-(AVD)

reference value for falling voltage is lower than the VIT+(AVD) reference value for rising

voltage in order to avoid parasitic detection (hysteresis).

The output of the AVD comparator is directly readable by the application software through a

real time status bit (AVDF) in the SICSR register. This bit is read only.

Monitoring the VDD main supply

The AVD threshold is selected by the AVD[1:0] bits in the AVDTHCR register.

If the AVD interrupt is enabled, an interrupt is generated when the voltage crosses the

VIT+(AVD) 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 microcontroller. See Figure 17.

The interrupt on the rising edge is used to inform the application that the VDD warning state

is over

Note:

Make sure the right combination of LVD and AVD thresholds is used as LVD and AVD levels

are not correlated. Refer to Table 47 on page 95 and Table 48 on page 96 for more details.

Figure 17.

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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