ATmega8U2/16U2/32U2
Assembly Code Example(1)
WDT_Prescaler_Change:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
in
r16, WDTCSR
ori
out
r16, (1<<WDCE) | (1<<WDE)
WDTCSR, r16
; -- Got four cycles to set the new values from here -
; Set new prescaler(time-out) value = 64K cycles (~0.5 s)
ldi
out
r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)
WDTCSR, r16
; -- Finished setting new values, used 2 cycles -
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_Prescaler_Change(void)
{
__disable_interrupt();
__watchdog_reset();
/* Start timed equence */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCSR = (1<<WDE) | (1<<WDP2) | (1<<WDP0);
__enable_interrupt();
}
Note:
1. The example code assumes that the part specific header file is included.
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.
10.5 Register Description
10.5.1
MCUSR – MCU Status Register
The MCU Status Register provides information on which reset source caused an MCU reset.
Bit
7
–
6
–
5
4
–
3
2
BORF
1
0
0x34 (0x54)
Read/Write
Initial Value
USBRF
WDRF
R/W
EXTRF
R/W
PORF
R/W
MCUSR
R
0
R
0
R
0
R/W
R/W
See Bit Description
• Bit 7:6 – Res: Reserved Bit
These bits are reserved and will always read as zero.
55
7799D–AVR–11/10
ATMEL [ ATMEL ]
