Datasheet

52
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
Figure 8-3. MCU Start-up, RESET Extended Externally
8.4 External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the minimum pulse
width (see Table 29-3 on page 386) will generate a reset, even if the clock is not running. Shorter pulses are not
guaranteed to generate a reset. When the applied signal reaches the Reset Threshold Voltage – V
RST
– on its
positive edge, the delay counter starts the MCU after the Time-out period – t
TOUT
– has expired.
Figure 8-4. External Reset During Operation
8.5 Brown-out Detection
ATmega16U4/ATmega32U4 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V
CC
level
during operation by comparing it to a fixed trigger level. The trigger level for the BOD can be selected by the
BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free Brown-out Detection. The hysteresis
on the detection level should be interpreted as V
BOT+
= V
BOT
+ V
HYST
/2 and V
BOT-
= V
BOT
- V
HYST
/2.
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
V
CC
V
POR
CC