Figure 14. Reset Logic
DATA BUS
MCU Control and Status
Register (MCUCSR)
Brown-Out
Reset Circuit
BODEN
BODLEVEL
Pull-up Resistor
SPIKE
FILTER
Watchdog
Oscillator
Delay Counters
Clock
CK
TIMEOUT
Generator
CKSEL[3:0]
SUT[1:0]
Table 15. Reset Characteristics
Symbol Parameter
Condition
Min
Typ
Max
Units
Power-on Reset Threshold
1.4
2.3
V
Voltage (rising)(1)
VPOT
Power-on Reset Threshold
Voltage (falling)
1.3
2.3
0.9
1.5
V
VRST
tRST
RESET Pin Threshold Voltage
0.1
VCC
µs
Minimum pulse width on
RESET Pin
Brown-out Reset Threshold
Voltage(2)
BODLEVEL = 1
BODLEVEL = 0
BODLEVEL = 1
BODLEVEL = 0
2.4
3.7
2.6
4.0
2
2.9
4.5
VBOT
V
Minimum low voltage period for
Brown-out Detection
µs
µs
tBOD
2
VHYST
Brown-out Detector hysteresis
130
mV
Notes: 1. The Power-on Reset will not work unless the supply voltage has been below VPOT
(falling).
2. 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 = 1 for ATmega8L and BODLEVEL = 0 for
ATmega8. BODLEVEL = 1 is not applicable for ATmega8.
36
ATmega8(L)
2486M–AVR–12/03
ATMEL [ ATMEL ]
