25.5 Entering the Boot Loader Program
Entering the Boot Loader takes place by a jump or call from the application program. This may
be initiated by a trigger such as a command received via USART, or SPI interface. Alternatively,
the Boot Reset Fuse can be programmed so that the Reset Vector is pointing to the Boot Flash
start address after a reset. In this case, the Boot Loader is started after a reset. After the applica-
tion code is loaded, the program can start executing the application code. Note that the fuses
cannot be changed by the MCU itself. This means that once the Boot Reset Fuse is pro-
grammed, the Reset Vector will always point to the Boot Loader Reset and the fuse can only be
changed through the serial or parallel programming interface.
Table 25-4. Boot Reset Fuse(1)
BOOTRST
Reset Address
1
0
Reset Vector = Application Reset (address 0x0000)
Reset Vector = Boot Loader Reset (see Table 25-6 on page 291)
Note:
1. “1” means unprogrammed, “0” means programmed
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ATmega169P
8018A–AVR–03/06
ATMEL [ ATMEL ]
