ATmega1280 Atmel Corporation, ATmega1280 Datasheet - Page 42

• Manufacturer Part Number: ATmega1280
• Manufacturer: Atmel Corporation

Specifications of ATmega1280

• Flash (kbytes): 128 Kbytes
• Pin Count: 100
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 86
• Ext Interrupts: 32
• Usb Speed: No
• Usb Interface: No
• Spi: 5
• Twi (i2c): 1
• Uart: 4
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 16
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 8
• Eeprom (bytes): 4096
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.8 to 5.5
• Operating Voltage (vcc): 1.8 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 6
• Output Compare Channels: 16
• Input Capture Channels: 4
• Pwm Channels: 15
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

10.3.1
10.3.2
10.4
2549N–AVR–05/11
Low Power Crystal Oscillator
Default Clock Source
Clock Start-up Sequence
The device is shipped with internal RC oscillator at 8.0MHz and with the fuse CKDIV8 pro-
grammed, resulting in 1.0MHz system clock. The startup time is set to maximum and time-out
period enabled. (CKSEL = "0010", SUT = "10", CKDIV8 = "0"). The default setting ensures that
all users can make their desired clock source setting using any available programming interface.
Any clock source needs a sufficient V
cycles before it can be considered stable.
To ensure sufficient V
the device reset is released by all other reset sources.
describes the start conditions for the internal reset. The delay (t
Oscillator and the number of cycles in the delay is set by the SUTx and CKSELx fuse bits. The
selectable delays are shown in
dependent as shown in
Table 10-2.
Main purpose of the delay is to keep the AVR in reset until it is supplied with minimum V
delay will not monitor the actual voltage and it will be required to select a delay longer than the
Vcc 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
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 consid-
ered 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.
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
assumed to be at a sufficient level and only the start-up time is included.
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
ceramic resonator may be used.
This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 out-
put. 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
Crystal Oscillator” on page
Typ Time-out (V
4.1ms
65ms
Number of Watchdog Oscillator Cycles
0ms
CC
= 5.0V)
CC
“Typical Characteristics” on page
, the device issues an internal reset with a time-out delay (t
44.
Table
ATmega640/1280/1281/2560/2561
CC
10-2. The frequency of the Watchdog Oscillator is voltage
Typ Time-out (V
to start oscillating and a minimum number of oscillating
CC
before it releases the reset, and the time-out delay
4.3ms
69ms
0ms
CC
= 3.0V)
Figure
“On-chip Debug System” on page 55
385.
TOUT
10-2. Either a quartz crystal or a
) is timed from the Watchdog
Number of Cycles
8K (8,192)
512
0
“Full Swing
TOUT
CC
) after
. The
CC
42
is