ATmega640 Atmel Corporation, ATmega640 Datasheet - Page 63

• Manufacturer Part Number: ATmega640
• Manufacturer: Atmel Corporation

Specifications of ATmega640

• Flash (kbytes): 64 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

12.4
12.4.1
12.4.2
2549N–AVR–05/11
Watchdog Timer
Features
Overview
ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three
conditions above to ensure that the reference is turned off before entering Power-down mode.
•
•
•
•
Figure 12-7. Watchdog Timer
ATmega640/1280/1281/2560/2561 has an Enhanced Watchdog Timer (WDT). The WDT is a
timer counting cycles of a separate on-chip 128kHz oscillator. The WDT gives an interrupt or a
system reset when the counter reaches a given time-out value. In normal operation mode, it is
required that the system uses the WDR - Watchdog Timer Reset - instruction to restart the coun-
ter before the time-out value is reached. If the system doesn't restart the counter, an interrupt or
system reset will be issued.
In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can be used
to wake the device from sleep-modes, and also as a general system timer. One example is to
limit the maximum time allowed for certain operations, giving an interrupt when the operation
has run longer than expected. In System Reset mode, the WDT gives a reset when the timer
expires. This is typically used to prevent system hang-up in case of runaway code. The third
mode, Interrupt and System Reset mode, combines the other two modes by first giving an inter-
rupt and then switch to System Reset mode. This mode will for instance allow a safe shutdown
by saving critical parameters before a system reset.
The Watchdog always on (WDTON) fuse, if programmed, will force the Watchdog Timer to Sys-
tem Reset mode. With the fuse programmed the System Reset mode bit (WDE) and Interrupt
mode bit (WDIE) are locked to 1 and 0 respectively. To further ensure program security, altera-
Clocked from separate On-chip Oscillator
3 Operating modes
Selectable Time-out period from 16ms to 8s
Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode
– Interrupt
– System Reset
– Interrupt and System Reset
WATCHDOG
RESET
OSCILLATOR
128 kHz
WDIF
WDIE
WDE
ATmega640/1280/1281/2560/2561
WDP0
WDP1
WDP2
WDP3
MCU RESET
INTERRUPT
63