Datasheet

Table 31-4. Boot Lock Bit1 Protection Modes (Boot Loader Section)

BLB1

Mode

BLB12 BLB11 Protection

1 1 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 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.

Note: “1” means unprogrammed, “0” means programmed.

31.7 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. The number of bits actually used is implementation dependent.

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

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.

ATmega328PB

BTLDR - Boot Loader Support – Read-While-Wri...

Datasheet Complete

DS40001906C-page 372