ATmega8 Atmel Corporation, ATmega8 Datasheet - Page 45

• Manufacturer Part Number: ATmega8
• Manufacturer: Atmel Corporation

Specifications of ATmega8

• Flash (kbytes): 8 Kbytes
• Pin Count: 32
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 12
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 23
• Ext Interrupts: 2
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• 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): 1
• Eeprom (bytes): 512
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 3
• Output Compare Channels: 3
• Input Capture Channels: 1
• Pwm Channels: 3
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

Timed Sequences
for Changing the
Configuration of
the Watchdog
Timer
Safety Level 1
(WDTON Fuse
Unprogrammed)
Safety Level 2
(WDTON Fuse
Programmed)
2486Z–AVR–02/11
The sequence for changing the Watchdog Timer configuration differs slightly between the safety
levels. Separate procedures are described for each level.
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit
to 1 without any restriction. A timed sequence is needed when changing the Watchdog Time-out
period or disabling an enabled Watchdog Timer. To disable an enabled Watchdog Timer and/or
changing the Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written
2. Within the next four clock cycles, in the same operation, write the WDE and WDP bits as
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A
timed sequence is needed when changing the Watchdog Time-out period. To change the
Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE
Within the next four clock cycles, in the same operation, write the WDP bits as desired, but with
the WDCE bit cleared. The value written to the WDE bit is irrelevant.
Assembly Code Example
C Code Example
to WDE regardless of the previous value of the WDE bit
desired, but with the WDCE bit cleared
always is set, the WDE must be written to one to start the timed sequence
WDT_off:
void WDT_off(void)
{
}
; reset WDT
WDR
; Write logical one to WDCE and WDE
in
ori r16, (1<<WDCE)|(1<<WDE)
out WDTCR, r16
; Turn off WDT
ldi r16, (0<<WDE)
out WDTCR, r16
ret
/* reset WDT */
_WDR();
/* Write logical one to WDCE and WDE */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
r16, WDTCR
ATmega8(L)
45