Rainbow-electronics AT90LS4433 Manual de usuario descargar pdf (Pagina 25)

AT90S/LS4433

1042G–AVR–09/02

Brown-out Detection AT90S4433 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

level during the operation. The power supply must be decoupled with a 47 nF to 100 nF

capacitor if the BOD function is used. The BOD circuit can be enabled/disabled by the

fuse BODEN. When BODEN is enabled (BODEN programmed), and V

decreases to a

value below the trigger level, the Brown-out Reset is immediately activated. When V

increases above the trigger level, the Brown-out Reset is deactivated after a delay. The

delay is defined by the user in the same way as the delay of POR signal (see Table 5).

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 of 50 mV to ensure spike-free Brown-out Detection.

The BOD circuit will only detect a drop in V

if the voltage stays below the trigger level

for longer than 3 µs for trigger level 4.0V, 7 µs for trigger level 2.7V (typical values).

Figure 28. Brown-out Reset during Operation

Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of one XTAL cycle

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

period (t

TOUT

). See page 43 for details on operation of the Watchdog.

Figure 29. Watchdog Reset during Operation

VCC

RESET

TIME-OUT

INTERNAL

RESET

BOT-

BOT+

TOUT

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Rainbow-electronics AT90LS4433 Manual de usuario Pagina 25