ATmega64A
10.0.5
Brown-out Detection
ATmega64A has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC level dur-
ing 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 VBOT+ = VBOT + VHYST/2 and VBOT-
BOT - VHYST/2.
=
V
The BOD circuit can be enabled/disabled by the fuse BODEN. When the BOD is enabled
(BODEN programmed), and VCC decreases to a value below the trigger level (VBOT- in Figure 10-
5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level
(VBOT+ in Figure 10-5), the delay counter starts the MCU after the Time-out period tTOUT has
expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for lon-
ger than tBOD given in Table 28-3.
Figure 10-5. Borwn-out Reset During Operation
V
V
BOT+
CC
V
BOT-
RESET
t
TOUT
TIME-OUT
INTERNAL
RESET
10.0.6
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. Refer to
page 55 for details on operation of the Watchdog Timer.
54
8160C–AVR–07/09
ATMEL [ ATMEL ]
