ATmega32(L)
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 15) 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 18. External Reset During Operation
CC
Brown-out Detection
ATmega32 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 selected by the fuse BODLEVEL to be 2.7V (BODLEVEL unprogrammed),
or 4.0V (BODLEVEL programmed). 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+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
The BOD circuit can be enabled/disabled by the fuse BODEN. When the BOD is
enabled (BODEN programmed), and VCC decreases to a value below the trigger level
(VBOT- in Figure 19), the Brown-out Reset is immediately activated. When VCC increases
above the trigger level (VBOT+ in Figure 19), the delay counter starts the MCU after the
Time-out period tTOUT has expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level
for longer than tBOD given in Table 15.
Figure 19. Brown-out Reset During Operation
V
V
BOT+
CC
V
BOT-
RESET
t
TOUT
TIME-OUT
INTERNAL
RESET
39
2503J–AVR–10/06
ATMEL [ ATMEL ]
