ATmega8HVA Atmel Corporation, ATmega8HVA Datasheet - Page 46

• Manufacturer Part Number: ATmega8HVA
• Manufacturer: Atmel Corporation

Specifications of ATmega8HVA

• Flash (kbytes): 8 Kbytes
• Pin Count: 28
• Max. Operating Frequency: 4 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 3
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 6
• Ext Interrupts: 3
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 6
• Adc Resolution (bits): 12
• Adc Speed (ksps): 1.9
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 0.5
• Eeprom (bytes): 256
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -20 to 85
• I/o Supply Class: 1.8 to 9.0
• Operating Voltage (vcc): 1.8 to 9.0
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 2
• Output Compare Channels: 4
• Input Capture Channels: 2
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

11.3
11.3.1
11.3.2
46
Watchdog Timer
ATmega8HVA/16HVA
Features
Overview
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ATmega8HVA/16HVA has an Enhanced Watchdog Timer (WDT). The WDT counts cycles of the
Ultra Low Power RC 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 counter before the time-out value is
reached. If the system doesn't restart the counter, an interrupt or system reset will be issued.
Figure 11-6. Watchdog Timer
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, alter-
ations to the Watchdog set-up must follow timed sequences. The sequence for clearing WDE
and changing time-out configuration is as follows:
Clocked from separate On-chip Oscillator
3 Operating modes
Selectable Time-out period from 16 ms to 8s
Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode
– Interrupt
– System Reset
– Interrupt and System Reset
Ultra Low Power RC
WATCHDOG
RESET
OSCILLATOR
WDIE
WDIF
WDE
WDP0
WDP1
WDP2
WDP3
MCU RESET
INTERRUPT
8024A–AVR–04/08