ATmega644 Atmel Corporation, ATmega644 Datasheet - Page 51

• Manufacturer Part Number: ATmega644
• Manufacturer: Atmel Corporation

Specifications of ATmega644

• Flash (kbytes): 64 Kbytes
• Pin Count: 44
• Max. Operating Frequency: 20 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 32
• Ext Interrupts: 32
• Usb Speed: No
• Usb Interface: No
• Spi: 3
• Twi (i2c): 1
• Uart: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 4
• Eeprom (bytes): 2048
• 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: 3
• Output Compare Channels: 6
• Input Capture Channels: 1
• Pwm Channels: 6
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

2593N–AVR–07/10
Note: If the Watchdog is accidentally enabled, for example by a runaway pointer or brown-out
condition, the device will be reset and the Watchdog Timer will stay enabled. If the code is not
set up to handle the Watchdog, this might lead to an eternal loop of time-out resets. To avoid this
situation, the application software should always clear the Watchdog System Reset Flag
(WDRF) and the WDE control bit in the initialisation routine, even if the Watchdog is not in use.
The following code example shows one assembly and one C function for changing the time-out
value of the Watchdog Timer.
Note:
Note: The Watchdog Timer should be reset before any change of the WDP bits, since a change
in the WDP bits can result in a time-out when switching to a shorter time-out period.
Assembly Code Example
C Code Example
WDT_Prescaler_Change:
void WDT_Prescaler_Change(void)
{
}
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
in
ori
out
; --
; Set new prescaler(time-out) value = 64K cycles (~0.5 s)
ldi
out
; --
; Turn on global interrupt
sei
ret
__disable_interrupt();
__watchdog_reset();
/* Start timed
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCSR
__enable_interrupt();
1. The example code assumes that the part specific header file is included.
r16, WDTCSR
r16, (1<<WDCE) | (1<<WDE)
WDTCSR, r16
Got four cycles to set the new values from here -
r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)
WDTCSR, r16
Finished setting new values, used 2 cycles -
= (1<<WDE) | (1<<WDP2) | (1<<WDP0);
(1)
(1)
equence */
ATmega644
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