Figure 8-2. MCU Start-up, RESET Tied to VCC
VPOT
VCC
VRST
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
Figure 8-3. MCU Start-up, RESET Extended Externally
VPOT
VCC
VRST
RESET
tTOUT
TIME-OUT
INTERNAL
RESET
8.0.4
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 8-1) 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 – VRST – on its positive edge, the delay counter starts the MCU after
the Time-out period – tTOUT – has expired.
Figure 8-4. External Reset During Operation
CC
8.0.5
60
Brown-out Detection
AT90USB64/128 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC level
during operation by comparing it to a fixed trigger level. The trigger level for the BOD can be
AT90USB64/128
7593A–AVR–02/06
ATMEL [ ATMEL ]
