ATMEGA8A-AUR Atmel, ATMEGA8A-AUR Datasheet - Page 42

• Manufacturer Part Number: ATMEGA8A-AUR
• Description: MCU AVR 8KB FLASH 16MHZ 32TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA8A-AUR

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 23
• Program Memory Size: 8KB (4K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 1K 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: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

10.5
10.5.1
10.5.2
8159D–AVR–02/11
Timed Sequences for Changing the Configuration of the Watchdog Timer
Safety Level 1 (WDTON Fuse Unprogrammed)
Safety Level 2 (WDTON Fuse Programmed)
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:
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:
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
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be writ-
2. Within the next four clock cycles, in the same operation, write the WDE and WDP bits
1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE
WDT_off:
void WDT_off(void)
{
}
ten to WDE regardless of the previous value of the WDE bit.
as desired, but with the WDCE bit cleared.
always is set, the WDE must be written to one to start the timed sequence.
; 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
ATmega8A
42