ATmega328P datasheet(48/448 Pages) ATMEL

48 / 448 page

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

Figure 10-3. MCU Start-up, RESET Extended Externally

10.4

External Reset

An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the

minimum pulse width (see ”System and Reset Characteristics” on page 318) 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 – V

RST – on its positive edge, the

delay counter starts the MCU after the Time-out period – t

TOUT – has expired. The External Reset

can be disabled by the RSTDISBL fuse, see Table 27-7 on page 296.

Figure 10-4. External Reset During Operation

10.5

Brown-out Detection

ATmega48PA/88PA/168PA/328P has an On-chip Brown-out Detection (BOD) circuit for moni-

toring the V

CC 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

BOT+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.When the BOD is enabled, and VCC

decreases to a value below the trigger level (V

BOT- in Figure 10-5 on page 49), the Brown-out

Reset is immediately activated. When V

CC increases above the trigger level (VBOT+ in Figure 10-

5 on page 49), the delay counter starts the MCU after the Time-out period t

TOUT has expired.

The BOD circuit will only detect a drop in V

CC if the voltage stays below the trigger level for lon-

ger than t

BOD given in ”System and Reset Characteristics” on page 318.

RESET

TIME-OUT

INTERNAL

RESET

TOUT

POT

RST

VCC

ATmega328P Datenblatt(PDF) 48 Page - ATMEL Corporation