ATMEGA640 datasheet(53/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

11.9.5

Watchdog Timer

If the Watchdog Timer is not needed in the application, the module should be turned off. If the Watchdog Timer is

enabled, it will be enabled in all sleep modes, and hence, always consume power. In the deeper sleep modes, this

will contribute significantly to the total current consumption. Refer to “Interrupts” on page 101 for details on how to

configure the Watchdog Timer.

11.9.6

Port Pins

When entering a sleep mode, all port pins should be configured to use minimum power. The most important is then

to ensure that no pins drive resistive loads. In sleep modes where both the I/O clock (clkI/O) and the ADC clock

(clkADC) are stopped, the input buffers of the device will be disabled. This ensures that no power is consumed by

the input logic when not needed. In some cases, the input logic is needed for detecting wake-up conditions, and it

will then be enabled. Refer to the section “Digital Input Enable and Sleep Modes” on page 71 for details on which

pins are enabled. If the input buffer is enabled and the input signal is left floating or have an analog signal level

close to VCC/2, the input buffer will use excessive power.

For analog input pins, the digital input buffer should be disabled at all times. An analog signal level close to VCC/2

on an input pin can cause significant current even in active mode. Digital input buffers can be disabled by writing to

the Digital Input Disable Registers (DIDR2, DIDR1 and DIDR0). Refer to “DIDR2 – Digital Input Disable Register 2”

on page 288, “DIDR1 – Digital Input Disable Register 1” on page 267, and “DIDR0 – Digital Input Disable Register

0” on page 287 for details.

11.9.7

On-chip Debug System

If the On-chip debug system is enabled by the OCDEN Fuse and the chip enters sleep mode, the main clock

source is enabled, and hence, always consumes power. In the deeper sleep modes, this will contribute significantly

to the total current consumption.

There are three alternative ways to disable the OCD system:

•

Disable the OCDEN Fuse

•

Disable the JTAGEN Fuse

•

Write one to the JTD bit in MCUCR

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