ATmega8(L)
page address is taken from the high part of the Z-pointer. The data in R1 and R0 are
ignored. The PGWRT bit will auto-clear upon completion of a page write, 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 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.
Bit
15
Z15
Z7
7
14
Z14
Z6
6
13
Z13
Z5
5
12
Z12
Z4
4
11
Z11
Z3
3
10
Z10
Z2
2
9
Z9
Z1
1
8
Z8
Z0
0
ZH (R31)
ZL (R30)
Since the Flash is organized in pages (see Table 93 on page 224), the Program Counter
can be treated as having two different sections. One section, consisting of the least sig-
nificant bits, is addressing the words within a page, while the most significant bits are
addressing the pages. This is shown in Figure 103. 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.
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2486M–AVR–12/03
ATMEL [ ATMEL ]
