atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 282

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

23.7.7
23.7.8
23.7.9
282
ATmega32/64/M1/C1
Setting the Boot Loader Lock Bits by SPM
EEPROM Write Prevents Writing to SPMCSR
Reading the Fuse and Lock Bits from Software
To set the Boot Loader Lock bits, write the desired data to R0, write “X0001001” to SPMCSR
and execute SPM within four clock cycles after writing SPMCSR. The only accessible Lock bits
are the Boot Lock bits that may prevent the Application and Boot Loader section from any soft-
ware update by the MCU.
See
Flash access.
If bits 5..2 in R0 are cleared (zero), the corresponding Boot 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 lO
is also recommended to set bits 7, 6, 1, and 0 in R0 to “1” when writing the Lock bits. When pro-
gramming the Lock bits the entire Flash can be read during the operation.
Note that an EEPROM write operation will block all software programming to Flash. Reading the
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.
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 LPM instruc-
tion 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 LPM instruction is executed
within three CPU cycles or no SPM instruction is executed within four CPU cycles. When BLB-
SET and SPMEN are cleared, LPM will work as described in the Instruction set Manual.
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 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 below. Refer to
detailed description and mapping of the Fuse Low byte.
Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM instruc-
tion is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR,
the value of the Fuse High byte (FHB) will be loaded in the destination register as shown below.
Refer to
When reading the Extended Fuse byte, load 0x0002 in the Z-pointer. When an LPM instruction
is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR, the
Bit
R0
Bit
Rd
Bit
Rd
Bit
Rd
Table 23-2
Table 24-6 on page 292
FLB7
FHB7
and
7
1
7
–
7
7
Table 23-3
FHB6
FLB6
6
6
6
1
6
–
for how the different settings of the Boot Loader bits affect the
for detailed description and mapping of the Fuse High byte.
BLB12
BLB12
FLB5
FHB5
5
5
5
5
BLB11
BLB11
FLB4
FHB4
4
4
4
4
BLB02
BLB02
FHB3
FLB3
3
3
3
3
BLB01
BLB01
FHB2
FLB2
2
2
2
2
ck
Table 24-4 on page 290
bits). For future compatibility it
FLB1
FHB1
LB2
1
1
1
1
1
FHB0
FLB0
LB1
0
1
0
0
0
7647A–AVR–02/08
for a