
265
ATmega64A [DATASHEET]
8160D–AVR–02/2013
mode 2) does not control the programming of the Flash memory by SPM instruction. Similarly, the general
Read/Write Lock (Lock bit mode 3) does not control reading nor writing by LPM/SPM, if it is attempted.
Note:
1. “1” means unprogrammed, “0” means programmed
Note:
1. “1” means unprogrammed, “0” means programmed
27.6
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 trig-
ger 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 application 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.
Note:
1. “1” means unprogrammed, “0” means programmed
Table 27-2.
Boot Lock Bit0 Protection Modes (Application Sectio
n)(1)BLB0 Mode
BLB02
BLB01
Protection
1
No restrictions for SPM or LPM accessing the Application section.
2
1
0
SPM is not allowed to write to the Application section.
3
0
SPM is not allowed to write to the Application section, and LPM executing from the
Boot Loader section is not allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts are disabled while
executing from the Application section.
4
0
1
LPM executing from the Boot Loader section is not allowed to read from the
Application section. If Interrupt Vectors are placed in the Boot Loader section,
interrupts are disabled while executing from the Application section.
Table 27-3.
Boot Lock Bit1 Protection Modes (Boot Loader Section)
BLB1 Mode
BLB12
BLB11
Protection
1
No restrictions for SPM or LPM accessing the Boot Loader section.
2
1
0
SPM is not allowed to write to the Boot Loader section.
3
0
SPM is not allowed to write to the Boot Loader section, and LPM executing from the
Application section is not allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts are disabled while executing
from the Boot Loader section.
4
0
1
LPM executing from the Application section is not allowed to read from the Boot
Loader section. If Interrupt Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
Table 27-4.
Boot Reset Fuse
BOOTRST
Reset Address
1
Reset Vector = Application Reset (address 0x0000)
0