279
4317I–AVR–01/08
AT90PWM2/3/2B/3B
For details about these two section, see
“NRWW – No Read-While-Write Section” on page 267
and
“RWW – Read-While-Write Section” on page 267
Note:
1. Z15:Z13: 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 272
for details about the use of
Z-pointer during Self-Programming.
25. Memory Programming
25.1
Program And Data Memory Lock Bits
The AT90PWM2/2B/3/3B provides six Lock bits which can be left unprogrammed (“1”) or can be
programmed (“0”) to obtain the additional features listed in
. The Lock bits can only be
erased to “1” with the Chip Erase command.
Table 24-8.
Explanation of Different Variables used in
and the Mapping to the Z-
pointer
Variable
Corresponding
Z-value
Description
PCMSB
11
Most significant bit in the Program Counter. (The
Program Counter is 12 bits PC[11:0])
PAGEMSB
4
Most significant bit which is used to address the
words within one page (32 words in a page requires
5 bits PC [4:0]).
ZPCMSB
Z12
Bit in Z-register that is mapped to PCMSB. Because
Z0 is not used, the ZPCMSB equals PCMSB + 1.
ZPAGEMSB
Z5
Bit in Z-register that is mapped to PAGEMSB.
Because Z0 is not used, the ZPAGEMSB equals
P 1.
PCPAGE
PC[11:5]
Z12:Z6
Program counter page address: Page select, for
page erase and page write
PCWORD
PC[4:0]
Z5:Z1
Program counter word address: Word select, for
filling temporary buffer (must be zero during page
write operation)
Table 25-1.
Lock Bit Byte
Lock Bit Byte
Bit No
Description
Default Value
7
–
1 (unprogrammed)
6
–
1 (unprogrammed)
BLB12
5
Boot Lock bit
1 (unprogrammed)
BLB11
4
Boot Lock bit
1 (unprogrammed)
BLB02
3
Boot Lock bit
1 (unprogrammed)
BLB01
2
Boot Lock bit
1 (unprogrammed)
LB2
1
Lock bit
1 (unprogrammed)
LB1
0
Lock bit
1 (unprogrammed)