Table 26-11. Explanation of Different Variables used in Figure 26-3 and the Mapping to the Z-
pointer, ATmega168
Corresponding
Variable
Z-value(1)
Description
Most significant bit in the Program Counter. (The
Program Counter is 12 bits PC[11:0])
PCMSB
12
5
Most significant bit which is used to address
the words within one page (64 words in a page
requires 6 bits PC [5:0])
PAGEMSB
ZPCMSB
Bit in Z-register that is mapped to PCMSB. Because
Z0 is not used, the ZPCMSB equals PCMSB + 1.
Z13
Z6
Bit in Z-register that is mapped to PAGEMSB.
Because Z0 is not used, the ZPAGEMSB equals
PAGEMSB + 1.
ZPAGEMSB
PCPAGE
Program counter page address: Page select, for
page erase and page write
PC[12:6]
PC[5:0]
Z13:Z7
Z6:Z1
Program counter word address: Word select, for
filling temporary buffer (must be zero during page
write operation)
PCWORD
Note:
1. Z15:Z14: always ignored
Z0: should be zero for all SPM commands, byte select for the LPM instruction.
See “Addressing the Flash During Self-Programming” on page 275 for details about the use of
Z-pointer during Self-Programming.
26.9 Register Description
26.9.1
SPMCSR – Store Program Memory Control and Status Register
The Store Program Memory Control and Status Register contains the control bits needed to con-
trol the Boot Loader operations.
Bit
7
SPMIE
R/W
0
6
5
–
4
RWWSRE
R/W
3
BLBSET
R/W
0
2
PGWRT
R/W
0
1
PGERS
R/W
0
0
RWWSB
SELFPRGEN
SPMCSR
0x37 (0x57)
Read/Write
Initial Value
R
0
R
0
R/W
0
0
• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the Status Register is set (one), the SPM
ready interrupt will be enabled. The SPM ready Interrupt will be executed as long as the SELF-
PRGEN bit in the SPMCSR Register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a Self-Programming (Page Erase or Page Write) operation to the RWW section is initi-
ated, the RWWSB will be set (one) by hardware. When the RWWSB bit is set, the RWW section
cannot be accessed. The RWWSB bit will be cleared if the RWWSRE bit is written to one after a
Self-Programming operation is completed. Alternatively the RWWSB bit will automatically be
cleared if a page load operation is initiated.
284
ATmega48/88/168
2545M–AVR–09/07
ATMEL [ ATMEL ]
