Datasheet

54
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
Figure 8-6. Watchdog Reset During Operation
8.7 USB Reset
When the USB controller is enabled and configured with the USB Reset CPU feature enabled and if a valid USB
Reset signalling is detected on the bus, the CPU core is reset but the USB controller remains enabled and
attached. This feature may be used to enhance device reliability.
Figure 8-7. USB Reset During Operation
8.8 Internal Voltage Reference
ATmega16U4/ATmega32U4 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.
8.8.1 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 8-3 on page 55. 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
CK
CC
CC
USB Traffic
USB Traffic
DP
DM
(USB Lines)
t
USBRSTMIN
End of Reset