ATMEGA6450-16AI(2004) データシートの表示（PDF） - Atmel Corporation
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ATMEGA6450-16AI Datasheet PDF : 347 Pages
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Port Pins
JTAG Interface and
On-chip Debug System
ATmega325/3250/645/6450
always consume power. In the deeper sleep modes, this will contribute significantly to
the total current consumption. Refer to “Watchdog Timer” on page 43 for details on how
to configure the Watchdog Timer.
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 buff-
ers 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 56 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 Regis-
ters (DIDR1 and DIDR0). Refer to “Digital Input Disable Register 1 – DIDR1” on page
192 and “Digital Input Disable Register 0 – DIDR0” on page 209 for details.
If the On-chip debug system is enabled by the OCDEN Fuse and the chip enter Power
down or Power save sleep mode, the main clock source remains enabled. In these
sleep modes, this will contribute significantly to the total current consumption. There are
three alternative ways to avoid this:
• Disable OCDEN Fuse.
• Disable JTAGEN Fuse.
• Write one to the JTD bit in MCUCSR.
The TDO pin is left floating when the JTAG interface is enabled while the JTAG TAP
controller is not shifting data. If the hardware connected to the TDO pin does not pull up
the logic level, power consumption will increase. Note that the TDI pin for the next
device in the scan chain contains a pull-up that avoids this problem. Writing the JTD bit
in the MCUCSR register to one or leaving the JTAG fuse unprogrammed disables the
JTAG interface.
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2570A–AVR–09/04
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