41
7530J–AVR–03/12
Atmel ATmega48/88/168 Automotive
7.7.6
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 (clk
I/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
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 V
CC/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 V
CC/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 (DIDR1 and
7.7.7
On-chip Debug System
If the On-chip debug system is enabled by the DWEN 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.
8.
System Control and Reset
8.0.1
Resetting the AVR
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. For the ATmega168, the instruction placed at the Reset Vector must be a
JMP – Absolute Jump – instruction to the reset handling routine. For the ATmega48 and
ATmega88, the instruction placed at the Reset Vector must be an RJMP – Relative Jump –
instruction to the reset handling routine. If the program never enables an interrupt source, the
Interrupt Vectors are not used, and regular program code can be placed at these locations. This
is also the case if the Reset Vector is in the Application section while the Interrupt Vectors are in
the Boot section or vice versa (ATmega88/168 only). The circuit diagram in
Figure 8-1 shows the
The I/O ports of the AVR are immediately reset to their initial state when a reset source goes
active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal
reset. This allows the power to reach a stable level before normal operation starts. The time-out
period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The dif-