before another reset occurs, the source of the reset can be found by examining the
Reset Flags.
Internal Voltage
Reference
ATmega640/1280/1281/2560/2561 features an internal bandgap reference. This refer-
ence 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 Table 26. 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 Com-
parator 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.
Table 26. Internal Voltage Reference Characteristics(1)
Symbol Parameter
Condition Min
Typ
1.1
40
Max Units
VBG
tBG
Bandgap reference voltage
TBD
TBD
TBD
TBD
70
V
Bandgap reference start-up time
µs
Bandgap reference current
consumption
IBG
TBD
10
TBD
µA
Note:
1. Values are guidelines only. Actual values are TBD.
62
ATmega640/1280/1281/2560/2561
2549A–AVR–03/05
ATMEL [ ATMEL ]
