Rainbow Electronics ATmega128RFA1 - Manual (Page 179)

179
8266A-MCU Wireless-12/09
ATmega128RFA1
Figure 13-5. Brown-out Reset During Operation
EVDD
RSTN
TIME-OUT
INTERNAL
RESET
t
TOUT
V
BOT-
V
BOT+
13.2.4 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 t
TOUT
. See "Watchdog Timer" on page 180 . for details on operation of the
Watchdog Timer.
Figure 13-6. Watchdog Reset During Operation
DEVDD
RSTN
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
1 CK Cycle
WDT
TIME-OUT
13.3 Internal Voltage Reference
ATmega128RFA1 features an internal bandgap reference. This reference is used for
Brown-out Detection, and it can be used as an input to the Analog Comparator or the
ADC.
Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used.
The start-up time is given in
"System and Reset Characteristics" on page 502 . To save
power, the reference is not always turned on. The reference is on during the following
situations:
1. When the BOD is enabled (by programming the BODLEVEL [2:0] Fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC,
the user must always allow the reference to start up before the output from the Analog
Comparator or ADC is used. To reduce power consumption in Power-down mode, the
user can avoid the three conditions above to ensure that the reference is turned off
before entering Power-down mode.