Datasheet

15. System Control and Reset

15.1 Resetting the AVR

During Reset, all I/O Registers are set to their initial values, and the program starts execution from the

Reset Vector. 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. The circuit diagram in

the following section shows the Reset Logic. The Table in System and Reset Characteristics defines the

electrical parameters of the reset circuitry.

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 CKSEL Fuses. The different selections for the delay period are

presented in Clock Sources.