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2513L–AVR–03/2013
ATmega162/V
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.
Note:
1. “1” means unprogrammed, “0” means programmed
Store Program
Memory Control
Register – SPMCR
The Store Program Memory Control Register contains the control bits needed to control the Boot
Loader operations.
Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the Status Register is set (one), the SPM
ready interrupt will be enabled. The SPM ready Interrupt will be executed as long as the SPMEN
bit in the SPMCR Register is cleared.
Bit 6 – RWWSB: Read-While-Write Section Busy
When a Self-programming (Page Erase or Page Write) operation to the RWW section is initi-
ated, the RWWSB will be set (one) by hardware. When the RWWSB bit is set, the RWW section
cannot be accessed. The RWWSB bit will be cleared if the RWWSRE bit is written to one after a
Self-programming operation is completed. Alternatively the RWWSB bit will automatically be
cleared if a page load operation is initiated.
Bit 5 – Res: Reserved Bit
This bit is a reserved bit in the ATmega162 and always read as zero.
Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (Page Erase or Page Write) to the RWW section, the RWW section is
blocked for reading (the RWWSB will be set by hardware). To re-enable the RWW section, the
user software must wait until the programming is completed (SPMEN will be cleared). Then, if
the RWWSRE bit is written to one at the same time as SPMEN, the next SPM instruction within
four clock cycles re-enables the RWW section. The RWW section cannot be re-enabled while
the Flash is busy with a Page Erase or a Page Write (SPMEN is set). If the RWWSRE bit is writ-
ten while the Flash is being loaded, the Flash load operation will abort and the data loaded will
be lost.
Table 91. Boot Reset Fuse
BOOTRST
Reset Address
1
Reset Vector = Application Reset (address 0x0000).
0
Bit
765
4
3
2
1
0
SPMIE
RWWSB
–
RWWSRE
BLBSET
PGWRT
PGERS
SPMEN
SPMCR
Read/Write
R/W
R
R/W
Initial Value
0