7.2.2 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 7-1) 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 7-4. External Reset during Operation
VCC
RESET
VRST
tTOUT
TIME-OUT
INTERNAL
RESET
7.2.3 Brown-out Detection
ATmega16/32/64/M1/C1 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 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
VBOT+ = VBOT + VHYST/2 and VBOT- = VBOT – VHYST/2.
Table 7-2. BODLEVEL Fuse Coding(1)(2)
BODLEVEL 2..0 Fuses
Typ VBOT
Disabled
4.5
Unit
111
110
011
100
010
001
101
000
V
V
V
V
V
V
V
4.4
4.3
4.2
2.8
2.7
2.6
Notes: 1. VBOT may be below nominal minimum operating voltage for some devices. For devices where this is the case,
the device is tested down to VCC = VBOT during the production test. This guarantees that a brown-out reset will
occur before VCC drops to a voltage where correct operation of the microcontroller is no longer guaranteed.
The test is performed using BODLEVEL = 010 for low operating voltage and BODLEVEL = 101 for high operat-
ing voltage.
2. Values are guidelines only.
Table 7-3. Brown-out Characteristics(1)
Parameter
Symbol
VHYST
tBOD
Min.
Typ.
80
2
Max.
Unit
mV
µs
Brown-out Detector Hysteresis
Min Pulse Width on Brown-out Reset
Note:
1. Values are guidelines only.
40
ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
