ATmega16 datasheet(40/357 Pages) ATMEL

40 / 357 page

2466S–AVR–05/09

ATmega16(L)

External Reset

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

minimum pulse width (see Table 15) 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.

Figure 18. External Reset During Operation

Brown-out Detection

ATmega16 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

CC level dur-

ing operation by comparing it to a fixed trigger level. The trigger level for the BOD can be

selected by the fuse BODLEVEL to be 2.7V (BODLEVEL unprogrammed), or 4.0V (BODLEVEL

programmed). The trigger level has a hysteresis to ensure spike free Brown-out Detection. The

hysteresis on the detection level should be interpreted as V

BOT+ = VBOT + VHYST/2 and VBOT- =

BOT - VHYST/2.

The BOD circuit can be enabled/disabled by the fuse BODEN. When the BOD is enabled

(BODEN programmed), and V

CC decreases to a value below the trigger level (VBOT- in Figure

19), the Brown-out Reset is immediately activated. When V

CC increases above the trigger level

BOT+ in Figure 19), the delay counter starts the MCU after the Time-out period tTOUT 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 Table 15.

Figure 19. Brown-out Reset During Operation

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

ATmega16 Datasheet(PDF) 40 Page - ATMEL Corporation