ATmega32U2 datasheet(55/314 Pages) ATMEL

55 / 314 page

7799B–AVR–07/09

ATmega8U2/16U2/32U2

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

10.5.1

MCUSR – MCU Status Register

The MCU Status Register provides information on which reset source caused an MCU reset.

• Bit 7:6 – Res: Reserved Bit

These bits are reserved and will always read as zero.

Assembly Code Example

(1)

WDT_Prescaler_Change:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Start timed sequence

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

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();

}

Bit

0x34 (0x54)

–

–USBRF

–

WDRF

BORF

EXTRF

PORF

MCUSR

Read/Write

R/W

Initial Value

See Bit Description

ATmega32U2 Datasheet(PDF) 55 Page - ATMEL Corporation

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