ATmega64A datasheet(286/392 Pages) ATMEL

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286

8160C–AVR–07/09

ATmega64A

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

26.7

Addressing the Flash During Self-programming

• The Z-pointer is used to address the SPM commands.

Since the Flash is organized in pages (see Table 27-9 on page 300), 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 Figure 26-3. Note that 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 program-

ming 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.

Table 26-4.

Boot Reset Fuse(1)

BOOTRST

Reset Address

Reset Vector = Application Reset (address 0x0000)

Reset Vector = Boot Loader Reset (see Table 26-6 on page 292)

Bit

151413121110

ZH (R31)

Z15

Z14

Z13

Z12

Z11

Z10

ZL (R30)

Z7Z6Z5Z4Z3Z2Z1Z0

76543210

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