Rainbow Electronics ATmega128L - Manual (Page 271)

271
ATmega128(L)
2467B–09/01
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 124 on page 283), 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 134. Note that the page erase
and page write operations are addressed independently. Therefore it is of major impor-
tance 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 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