Rainbow Electronics ATmega163L - Manual (Page 25)

ATmega163(L)
25
Brown-out Detection
ATmega163 has an on-chip brown-out detection (BOD) circuit for monitoring the V
CC
level during the operation. The BOD
circuit can be enabled/disabled by the fuse BODEN. When the BOD is enabled (BODEN programmed), and V
CC
decreases
to a value below the trigger level, the brown-out reset is immediately activated. When V
CC
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 sig-
nal, in 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
CC
if the voltage stays below the trigger level for longer than 9 µs for trigger level
4.0V, 21 µs for trigger level 2.7V (typical values).
Figure 28. Brown-out Reset During Operation
The hysteresis on V
BOT
: V
BOT+
= V
BOT
+ 25 mV, V
BOT-
= V
BOT
- 25 mV
Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of 1 XTAL cycle duration. On the falling edge of this
pulse, the delay timer starts counting the Time-out period t
TOUT
. Refer to page 51 for details on operation of the Watchdog
Timer.
Figure 29. Watchdog Reset During Operation
VCC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT
1 CK Cycle