Rainbow-electronics ATmega128L Manual de usuario descargar pdf (Pagina 48)

ATmega128(L)

2467B–09/01

Figure 24. External Reset During Operation

Brown-out Detection ATmega128 has an on-chip brown-out detection (BOD) circuit for monitoring the V

level during operation by comparing it to a fixed trigger level. The trigger level for the

BOD can be selected by the fuse BODLEVEL to be 2.7V (BODLEVEL unprogrammed),

or 4.0V (BODLEVEL programmed). The trigger level has a hysteresis to ensure spike

free brown-out detection. The hysteresis on the detection level should be interpreted as

BOT+

= V

BOT

+ V

HYST

/2 and V

BOT-

= V

BOT

- V

HYST

/2.

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

enabled (BODEN programmed), and V

decreases to a value below the trigger level

BOT-

in Figure 25), the Brown-out reset is immediately activated. When V

increases

above the trigger level (V

BOT+

in Figure 25), the delay counter starts the MCU after the

time-out period t

TOUT

has expired.

The BOD circuit will only detect a drop in V

if the voltage stays below the trigger level

for longer than t

BOD

given in Table 19.

Figure 25. Brown-out Reset During Operation

Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of 1 CK cycle dura-

tion. On the falling edge of this pulse, the delay timer starts counting the Time-out period

TOUT

. Refer to page 50 for details on operation of the Watchdog Timer.

RESET

TIME-OUT

INTERNAL

RESET

BOT-

BOT+

TOUT

1 2 ... 43 44 45 46 47 48 49 50 51 52 53 ... 330 331

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Rainbow-electronics ATmega128L Manual de usuario Pagina 48

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