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Atmel AT89C51ID2 Data Sheet - Keil

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Figure 12. Power Fail Detect<br />

Vcc<br />

4289A–8051–09/03<br />

Reset<br />

Vcc<br />

<strong>AT89C51ID2</strong><br />

The Power fail detect monitor the supply generated by the voltage regulator and generate<br />

a reset if this supply falls below a safety threshold as illustrated in the Figure 12<br />

below.<br />

When the power is applied, the Power Monitor immediately asserts a reset. Once the<br />

internal supply after the voltage regulator reach a safety level, the power monitor then<br />

looks at the XTAL clock input. The internal reset will remain asserted until the Xtal1 levels<br />

are above and below VIH and VIL. Further more. An internal counter will count 1024<br />

clock periods before the reset is de-asserted.<br />

If the internal power supply falls below a safety level, a reset is immediately asserted.<br />

t<br />

35

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