ST7MC1K2-Auto datasheet(49/371 Pages) STMICROELECTRONICS

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6.5.2

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 supply. The VIT- reference value for falling

voltage is lower than the VIT+ 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.

Caution:

The AVD function is active only if the LVD is enabled through the option byte (see

Section 14.1 on page 356).

Monitoring the VDD main supply

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

VIT+(AVD) or VIT-(AVD) threshold (AVDF bit toggles).

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 14.

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

is over.

If the voltage rise time trv is less than 256 or 4096 CPU cycles (depending on the reset delay

selected by option byte), no AVD interrupt is generated when VIT+(AVD) is reached.

If trv is greater than 256 or 4096 cycles then:

●

If the AVD interrupt is enabled before the VIT+(AVD) threshold is reached, then two AVD

interrupts are received: the first when the AVDIE bit is set, and the second when the

threshold is reached.

●

If the AVD interrupt is enabled after the VIT+(AVD) threshold is reached then only one

AVD interrupt occurs.

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