ATmega165 datasheet(238/336 Pages) ATMEL

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238

ATmega165/V

2573G–AVR–07/09

• Bit 1 – PGERS: Page Erase

If this bit is written to one at the same time as SPMEN, the next SPM instruction within

four clock cycles executes Page Erase. The page address is taken from the high part of

the Z-pointer. The data in R1 and R0 are ignored. The PGERS bit will auto-clear upon

completion of a Page Erase, or if no SPM instruction is executed within four clock

cycles. The CPU is halted during the entire Page Write operation if the NRWW section is

addressed.

• Bit 0 – SPMEN: Store Program Memory Enable

This bit enables the SPM instruction for the next four clock cycles. If written to one

together with either RWWSRE, BLBSET, PGWRT’ or PGERS, the following SPM

instruction will have a special meaning, see description above. If only SPMEN is written,

the following SPM instruction will store the value in R1:R0 in the temporary page buffer

addressed by the Z-pointer. The LSB of the Z-pointer is ignored. The SPMEN bit will

auto-clear upon completion of an SPM instruction, or if no SPM instruction is executed

within four clock cycles. During Page Erase and Page Write, the SPMEN bit remains

high until the operation is completed.

Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the

lower five bits will have no effect.

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 105 on page 249), the Program Coun-

ter 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 110. 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 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.

Bit

151413

121110

ZH (R31)

Z15

Z14

Z13

Z12

Z11

Z10

ZL (R30)

Z7Z6Z5Z4Z3

Z2Z1Z0

765

432

ATmega165 Datasheet(PDF) 238 Page - ATMEL Corporation

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