Datasheet

Figure 15-1. Reset Logic
MCU Status
Register (MCUSR)
Brown-out
Reset Circuit
BODLEVEL [2..0]
Delay Counters
CKSEL[3:0]
CK
TIMEOUT
WDRF
BORF
EXTRF
PORF
DATA BUS
Clock
Generator
SPIKE
FILTER
Pull-up Resistor
Watchdog
Oscillator
SUT[1:0]
Power-on Reset
Circuit
RSTDISBL
15.3 Power-on Reset
A Power-on Reset (POR) pulse is generated by an on-chip detection circuit. The POR is activated
whenever V
CC
is below the detection level. The POR circuit can be used to trigger the start-up Reset, as
well as to detect a failure in supply voltage.
A POR circuit ensures that the device is reset from power-on. Reaching the POR threshold voltage
invokes the delay counter, which determines how long the device is kept in Reset after V
CC
rise. The
Reset signal is activated again, without any delay, when V
CC
decreases below the detection level.
Figure 15-2. MCU Start-up, RESET Tied to V
CC
V
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
CC
ATmega48PA/88PA/168PA
System Control and Reset
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40002011A-page 79