ATMEGA644PV ATMEL [ATMEL Corporation], ATMEGA644PV Datasheet - Page 283
ATMEGA644PV
Manufacturer Part Number
ATMEGA644PV
Description
8-bit Microcontroller with 16/32/64K Bytes In-System Programmable Flash
Manufacturer
ATMEL [ATMEL Corporation]
Datasheet
1.ATMEGA644PV.pdf
(408 pages)
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24.8.11
24.8.12
8011D–AVR–02/07
Preventing Flash Corruption
Programming Time for Flash when Using SPM
instruction is executed within three CPU cycles. When SIGRD and SPMEN are cleared, LPM will
work as described in the Instruction set Manual.
Table 24-5.
Note:
During periods of low V
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 correctly. 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
2. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
3. Keep the AVR core in Power-down sleep mode during periods of low V
The calibrated RC Oscillator is used to time Flash accesses.
typical programming time for Flash accesses from the CPU.
Table 24-6.
Note:
Signature Byte
Device Signature Byte 1
Device Signature Byte 2
Device Signature Byte 3
RC Oscillator Calibration Byte
Flash write (Page Erase, Page Write, and
write Lock bits by SPM)
bits to prevent any Boot Loader software updates.
This can be done by enabling the internal Brown-out Detector (BOD) if the operating volt-
age matches the detection level. If not, an external low V
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.
vent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCSR Register and thus the Flash from unintentional writes.
All other addresses are reserved for future use.
1. Minimum and maximum programming times is per individual operation.
Signature Row Addressing
SPM Programming Time
Symbol
CC
, the Flash program can be corrupted because the supply voltage is
(1)
Min Programming Time
ATmega164P/324P/644P
Z-Pointer Address
0x0000
0x0002
0x0004
0x0001
3.7 ms
CC
Table 24-6 on page 283
reset protection circuit can be
Max Programming Time
CC
. This will pre-
4.5 ms
shows the
283
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