Datasheet

ATmega16U4/32U4 [DATASHEET]

Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016

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.

Assembly Code Example

(1)

WDT_Prescaler_Change:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Start timed sequence

in r16, WDTCSR

ori r16, (1<<WDCE) | (1<<WDE)

out WDTCSR, r16

; -- Got four cycles to set the new values from

here -

; Set new prescaler(time-out) value = 64K cycles

(~0.5 s)

ldi r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)

out 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 sequence */

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();

}