ATMEGA48-20AI Atmel, ATMEGA48-20AI Datasheet - Page 48

• Manufacturer Part Number: ATMEGA48-20AI
• Description: IC AVR MCU 4K 5V 20MHZ 32-TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA48-20AI

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 23
• Program Memory Size: 4KB (2K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 512 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-TQFP, 32-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: ATMEGA48-24AI; ATMEGA48-24AI

10.8
10.8.1
48
Watchdog Timer
ATmega48/88/168
Features
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user
must always allow the reference to start up before the output from the Analog Comparator or
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.
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Figure 10-7. Watchdog Timer
ATmega48/88/168 has an Enhanced Watchdog Timer (WDT). The WDT is a timer counting
cycles of a separate on-chip 128 kHz 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.
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.
Clocked from separate On-chip Oscillator
3 Operating modes
Selectable Time-out period from 16 ms to 8 s
Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode
– Interrupt
– System Reset
– Interrupt and System Reset
WATCHDOG
RESET
OSCILLATOR
128 kHz
WDIE
WDIF
WDE
WDP0
WDP1
WDP2
WDP3
MCU RESET
INTERRUPT
2545S–AVR–07/10