Preventing flash corruption, Atmega162/v – Rainbow Electronics ATmega162V User Manual
Page 225
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ATmega162/V
2513E–AVR–09/03
executed within four CPU cycles. When BLBSET 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 SPMCR. When an LPM instruction is executed
within three cycles after the BLBSET and SPMEN bits are set in the SPMCR, the value
of the Fuse Low byte (FLB) will be loaded in the destination register as shown below.
Refer to Table 101 on page 232 for a 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
instruction is executed within three cycles after the BLBSET and SPMEN bits are set in
the SPMCR, the value of the Fuse High byte (FHB) will be loaded in the destination reg-
ister as shown below. Refer to Table 99 on page 231 for detailed description and
mapping of the Fuse High byte.
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 SPMCR, the value of the Extended Fuse byte (EFB) will be loaded in the destination
register as shown below. Refer to Table 99 on page 231 for detailed description and
mapping of the Extended Fuse byte.
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that
are unprogrammed, will be read as one.
Preventing Flash Corruption
During periods of low V
CC
, the Flash program can be corrupted because the supply volt-
age is too low for the CPU and the Flash to operate properly. These issues are the same
as for board level systems using the Flash, and the same design solutions should be
applied.
A Flash program corruption can be caused by two situations when the voltage is too low.
First, a regular write sequence to the Flash requires a minimum voltage to operate cor-
rectly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage
for executing instructions is too low.
Flash corruption can easily be avoided by following these design recommendations (one
is sufficient):
1.
If there is no need for a Boot Loader update in the system, program the Boot
Loader Lock bits to prevent any Boot Loader software updates.
2.
Keep the AVR RESET active (low) during periods of insufficient power supply
voltage. This can be done by enabling the internal Brown-out Detector (BOD) if
the operating voltage matches the detection level. If not, an external low V
CC
Reset Protection circuit can be used. If a Reset occurs while a write operation is
in progress, the write operation will be completed provided that the power supply
voltage is sufficient.
Bit
7
6
5
4
3
2
1
0
Rd
–
–
BLB12
BLB11
BLB02
BLB01
LB2
LB1
Bit
7
6
5
4
3
2
1
0
Rd
FLB7
FLB6
FLB5
FLB4
FLB3
FLB2
FLB1
FLB0
Bit
7
6
5
4
3
2
1
0
Rd
FHB7
FHB6
FHB5
FHB4
FHB3
FHB2
FHB1
FHB0
Bit
7
6
5
4
3
2
1
0
Rd
–
–
–
EFB4
EFB3
EFB2
EFB1
–