Datasheet

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. The fuses cannot be changed by the MCU itself. This means that
once the Boot Reset Fuse is programmed, 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 27-4. Boot Reset Fuse
BOOTRST Reset Address
1 Reset Vector = Application Reset (address 0x0000)
0 Reset Vector = Boot Loader Reset, as described by the Boot Loader Parameters
Note: '1' means unprogrammed, '0' means programmed.
27.7. Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers ZL and
ZH in the register file, and RAMPZ in the I/O space. The number of bits actually used is implementation
dependent. Note that the RAMPZ register is only implemented when the program space is larger than
64Kbytes.
Bit 15 14 13 12 11 10 9 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30) Z7 Z6 Z5 Z4 Z3 Z2 Z1 Z0
7 6 5 4 3 2 1 0
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30) Z7 Z6 Z5 Z4 Z3 Z2 Z1 Z0
7 6 5 4 3 2 1 0
RAMPZ7
RAMPZ6 RAMPZ5
RAMPZ4
RAMPZ3
RAMPZ2 RAMPZ1
RAMPZ0
Bit
23
22 21
20 19 18
17
16
15
14
13
12 11
10 9 8
Since the Flash is organized in pages, the Program Counter can be treated as having two different
sections. One section, consisting of the least significant bits, is addressing the words within a page, while
the most significant bits are addressing the pages. This is shown in the following figure. The Page Erase
and Page Write operations are addressed independently. Therefore it is of major importance that the Boot
Loader software addresses the same page in both the Page Erase and Page Write operation. Once a
programming operation is initiated, the address is latched and the Z-pointer can be used for other
operations.
The only SPM operation that does not use the Z-pointer is Setting the Boot Loader Lock bits. The content
of the Z-pointer is ignored and will have no effect on the operation. The LPM instruction does also use the
Z-pointer to store the address. Since this instruction addresses the Flash byte-by-byte, also the LSB (bit
Z0) of the Z-pointer is used.
Atmel ATmega16M1/32M1/64M1 [DATASHEET]
Atmel-8209F-ATmega16M1/32M1/64M1_Datasheet_Complete-10/2016
361