
51
7674F–AVR–09/09
ATmega164P/324P/644P
Figure 1. MCU Start-up, RESET Tied to VCC
Figure 2. MCU Start-up, RESET Extended Externally
Table 1. Power On Reset Specifications
Note:
1. Before rising, the supply has to be between
V
PORMIN and VPORMAX to ensure a Reset.
9.0.4
External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the
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 – V
RST – on its positive edge, the
delay counter starts the MCU after the Time-out period – t
TOUT – has expired.
Symbol
Parameter
Min
Typ
Max
Units
V
POT
Power-on Reset Threshold Voltage (rising)
1.1
1.4
1.7
V
Power-on Reset Threshold Voltage (falling)(1)
0.8
1.3
1.6
V
VPORMAX
VCC Max. start voltage to ensure internal
Power-on Reset signal
0.4
V
VPORMIN
VCC Min. start voltage to ensure internal
Power-on Reset signal
-0.1
V
VCCRR
VCC Rise Rate to ensure Power-on Reset
0.01
V/ms
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
RST
V
PORMA
X
VCC
CCRR
V
PORMIN
RESET
TIME-OUT
INTERNAL
RESET
tTOUT
VRST
VCC