Rainbow-electronics ATmega8515L Manual do Utilizador descarregar pdf (Página 167)

167

ATmega8515(L)

2512A–AVR–04/02

• Bit1–PGERS:PageErase

If thisbit iswritten to one at the same time asSPMEN, thenext SPM instruction within

fourclock cycles executes Page Erase. The page address is taken from the highpartof

the Z-pointer.The data in R1 and R0 areignored.ThePGERSbit will auto-clear upon

completion of aPageErase, or if no SPM instruction is executedwithin fourclock

cycles.The CPU ishaltedduring the entire page write operation if the NRWW section is

addressed.

• Bit 0 – SPMEN: Store Program Memory Enable

Thisbit enables the SPM instruction for thenext fourclock cycles. If writtentoone

togetherwith either RWWSRE, BLBSET, PGWRT’ or PGERS, the following SPM

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

the following SPM instruction will storethevalue in R1:R0 in thetemporary page buffer

addressedbythe 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 fourclock cycles. During Page Eraseand Page Write, the SPMEN bit remains

high until theoperation iscompleted.

Writing any othercombination than “10001”, “01001”, “00101”, “00011”, or “00001” in

the lowerfive bitswill havenoeffect.

Addressing the Flash

During Self-

Programming

The Z-pointer is used to address the SPMcommands.

Sincethe Flash is organized in pages(see Table89 on page 179), theProgram Counter

can betreated ashaving two different sections. One section,consisting of the least sig-

nificant bits, is addressing the words within a page,whilethemost significant bits are

addressing the pages.This isshowninFigure 73. Note that the Page Eraseand Page

Write operations areaddressed independently.Thereforeitis of major importancethat

the Boot Loadersoftwareaddresses the same page in both thePageEraseand Page

Write operation. Onceaprogramming operation is initiated, theaddress islatched and

the Z-pointercan beusedfor other operations.

Theonly SPM operation that does not usethe Z-pointer isSetting the Boot LoaderLock

bits.The content of the Z-pointer is ignored andwill havenoeffectontheoperation. The

LPM instruction does alsousethe Z-pointer to storetheaddress. Sincethis instruction

addresses the Flash byte by byte, alsothe LSB (bit Z0) of the Z-pointer is used.

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

76543 210

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Rainbow-electronics ATmega8515L Manual do Utilizador Página 167