Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Ficha De Dados
Códigos do produto
MEGA328P-XMINI
29
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
Main purpose of the delay is to keep the AVR in reset until it is supplied with minimum V
CC
. The delay will not
monitor the actual voltage and it will be required to select a delay longer than the V
CC
rise time. If this is not
possible, an internal or external Brown-Out Detection circuit should be used. A BOD circuit will ensure sufficient
V
V
CC
before it releases the reset, and the time-out delay can be disabled. Disabling the time-out delay without
utilizing a Brown-Out Detection circuit is not recommended.
The oscillator is required to oscillate for a minimum number of cycles before the clock is considered stable. An
internal ripple counter monitors the oscillator output clock, and keeps the internal reset active for a given
number of clock cycles. The reset is then released and the device will start to execute. The recommended
oscillator start-up time is dependent on the clock type, and varies from 6 cycles for an externally applied clock to
32K cycles for a low frequency crystal.
internal ripple counter monitors the oscillator output clock, and keeps the internal reset active for a given
number of clock cycles. The reset is then released and the device will start to execute. The recommended
oscillator start-up time is dependent on the clock type, and varies from 6 cycles for an externally applied clock to
32K cycles for a low frequency crystal.
The start-up sequence for the clock includes both the time-out delay and the start-up time when the device
starts up from reset. When starting up from Power-save or Power-down mode, V
starts up from reset. When starting up from Power-save or Power-down mode, V
CC
is assumed to be at a
sufficient level and only the start-up time is included.
9.3
Low Power Crystal Oscillator
Pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for
use as an On-chip Oscillator, as shown in
use as an On-chip Oscillator, as shown in
. Either a quartz crystal or a ceramic resonator
may be used.
This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 output. It gives the
lowest power consumption, but is not capable of driving other clock inputs, and may be more susceptible to
noise in noisy environments. In these cases, refer to the
lowest power consumption, but is not capable of driving other clock inputs, and may be more susceptible to
noise in noisy environments. In these cases, refer to the
.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the capacitors
depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of
the environment. Some initial guidelines for choosing capacitors for use with crystals are given in
depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of
the environment. Some initial guidelines for choosing capacitors for use with crystals are given in
. For ceramic resonators, the capacitor values given by the manufacturer should be used.
Figure 9-2.
Crystal Oscillator Connections
The Low Power Oscillator can operate in three different modes, each optimized for a specific frequency range.
The operating mode is selected by the fuses CKSEL3...1 as shown in
The operating mode is selected by the fuses CKSEL3...1 as shown in
.
Table 9-2.
Number of Watchdog Oscillator Cycles
Typ Time-out (V
CC
= 5.0V)
Typ Time-out (V
CC
= 3.0V)
Number of Cycles
0ms
0ms
0
4.1ms
4.3ms
512
65ms
69ms
8K (8,192)
XTAL2 (TOSC2)
XTAL1 (TOSC1)
GND
C2
C1