Rainbow Electronics ATmega161L - Manual (Page 27)

27
ATmega161(L)
1228C–AVR–08/02
Power-on Reset A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detec-
tion level is nominally 1.4V (rising V
CC
). 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
detect a failure in supply voltage.
A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reach-
ing the Power-on Reset threshold voltage invokes a delay counter, which determines
the delay, for which the device is kept in RESET after V
CC
rise. The time-out period of
the delay counter can be defined by the user through the CKSEL fuses. The eight differ-
ent selections for the delay period are presented in Table 4. The RESET signal is
activated again, without any delay, when the V
CC
decreases below detection level.
Figure 25. MCU Start-up, RESET Tied to V
CC
Figure 26. MCU Start-up, RESET Controlled Externally
VCC
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
VCC
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST