Rainbow-electronics ATmega64L Manual de usuario descargar pdf (Pagina 36)

ATmega16(L)

2466B–09/01

Power-on Reset A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detec-

tion level is defined in Table 15. The POR is activated whenever V

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 Power-on Reset (POR) circuit ensures that the device is reset from power-on. Reach-

ing the power-on reset threshold voltage invokes the delay counter, which determines

how long the device is kept in RESET after V

rise. The RESET signal is activated

again, without any delay, when V

decreases below the detection level.

Figure 16. MCU Start-up, RESET

Tied to V

Figure 17. MCU Start-up, RESET

Extended Externally

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.

RESET

TIME-OUT

INTERNAL

RESET

TOUT

POT

RST

RESET

TIME-OUT

INTERNAL

RESET

TOUT

POT

RST

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Rainbow-electronics ATmega64L Manual de usuario Pagina 36