Rainbow-electronics ATmega8515L Instrukcja Użytkownika Pobierz pdf (Strona 45)

ATmega8515(L)

2512A–AVR–04/02

External Reset An External Reset is generatedbya lowlevel on theRESET pin. Reset pulseslonger

than theminimumpulse width(see Table18)will generate a reset, even if the clock is

not running. Shorterpulses arenotguaranteed to generate a reset. When theapplied

signalreaches theReset Threshold Voltage – V

RST

–onitspositive edge, the delay

counterstarts the MCU after theTime-out period t

TOUT

has expired.

Figure 24. External Reset During Operation

Brown-out Detection ATmega8515 has an On-chipBrown-out Detection (BOD) circuit for monitoring theV

levelduring operation by comparingittoafixed triggerlevel.Thetriggerlevelfor the

BOD can be selectedbythe fuse BODLEVEL to be2.7V (BODLEVEL unprogrammed),

or 4.0V (BODLEVEL programmed).Thetriggerlevelhas a hysteresis to ensure spike

free Brown-out Detection. The hysteresis on the detection levelshould beinterpreted as

BOT+

= V

BOT

+ V

HYST

/2 and V

BOT-

= V

BOT

- V

HYST

/2.

The BOD circuit can be enabled/disabledbythe fuse BODEN. When the BOD is

enabled(BODENprogrammed), and V

decreases to a value below thetriggerlevel

BOT-

in Figure25), the Brown-out Reset is immediately activated. When V

increases

above thetriggerlevel(V

BOT+

in Figure25), the delaycounterstarts the MCU after the

time-out period t

TOUT

has expired.

The BOD circuit will only detectadrop in V

if thevoltage stays below thetriggerlevel

forlonger than t

BOD

giveninTable 18.

Figure 25. Brown-out Reset During Operation

RESET

TIME-OUT

INTERNAL

RESET

BOT-

BOT+

TOUT

1 2 ... 40 41 42 43 44 45 46 47 48 49 50 ... 222 223

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