
491
42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
30.6.6 Prevent Reading the RWW Section During Self-Programming
During Self-Programming (either Page Erase or Page Write), the RWW section is
always blocked for reading. The user software itself must prevent that this section is
addressed during the self programming operation. The RWWSB in the SPMCSR will be
set as long as the RWW section is busy. During Self-Programming the Interrupt Vector
interrupts must be disabled. Before addressing the RWW section after the programming
is completed, the user software must clear the RWWSB by writing the RWWSRE. See
30.6.7 Setting the Boot Loader Lock Bits by SPM
To set the Boot Loader Lock bits and general Lock bits, write the desired data to R0,
write “X0001001” to SPMCSR and execute SPM within four clock cycles after writing
SPMCSR.
Bit
7
6
5
4
3
2
1
0
R0
1
BLB12
BLB11
BLB02
BLB01
LB2
LB1
the Flash access.
If bits 5:0 in R0 are cleared (zero), the corresponding Lock bit will be programmed if an
SPM instruction is executed within four cycles after BLBSET and SPMEN are set in
SPMCSR. The Z-pointer is don’t care during this operation, but for future compatibility it
is recommended to load the Z-pointer with 0x0001 (same as used for reading the Lock
bits). For future compatibility it is also recommended to set bits 7 and 6 in R0 to “1”
when writing the Lock bits. When programming the Lock bits the entire Flash can be
read during the operation.
30.6.8 EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash.
Reading the Signature Row, Fuses and Lock bits from software will also be prevented
during the EEPROM write operation. It is recommended that the user checks the status
bit (EEPE) in the EECR Register and verifies that the bit is cleared before writing to the
SPMCSR Register.
30.6.9 Reading the Fuse and Lock Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits,
load the Z-pointer with 0x0001 and set the BLBSET and SPMEN bits in SPMCSR.
When an (E)LPM instruction is executed within three CPU cycles after the BLBSET and
SPMEN bits are set in SPMCSR, the value of the Lock bits will be loaded in the
destination register. The BLBSET and SPMEN bits will auto-clear upon completion of
reading the Lock bits or if no (E)LPM instruction is executed within three CPU cycles or
no SPM instruction is executed within four CPU cycles. When BLBSET and SPMEN are
cleared, (E)LPM will work as described in the Instruction Set Manual.
Bit
7
6
5
4
3
2
1
0
Rd
-
BLB12
BLB11
BLB02
BLB01
LB2
LB1
The algorithm for reading the Fuse Low byte is similar to the one described above for
reading the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and
set the BLBSET and SPMEN bits in SPMCSR. When an (E)LPM instruction is executed
within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR, the
value of the Fuse Low byte (FLB) will be loaded in the destination register as shown on