Datasheet

179
ATmega323(L)
1457E–11/01
cycles. During page erase and page write, the SPMEN bit remains high until the opera-
tion is completed.
Writing any other combination than “10001”, “01001”, “00101”, or “00001” in the lower
five bits will have no effect.
Preventing Flash
Corruption
During periods of low V
CC
, the Flash can be corrupted because the supply voltage 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 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. Keep the AVR RESET active (low) during periods of insufficient power supply
voltage. This can be done be 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. The total reset time must be longer than the Flash write
time. This can be achieved by holding the external reset, or by selecting a long
reset timeout.
2. Keep the AVR core in Power-down Sleep Mode during periods of low V
CC
. This
will prevent the CPU from attempting to decode and execute instructions, effec-
tively protecting the Flash from unintentional writes.
Assembly code example for a
Boot Loader
;- the routine writes one page of data from RAM to Flash the first data
: location in RAM is pointed to by the Y pointer (lowest address) the first
; data location in Flash is pointed to by the Z pointer (lowest address)
; - error handling is not included - the routine must be placed inside the
; boot space. Only code inside boot loader section should be read during
; self-programming.
;- registers used: r0, r1, temp1, temp2, looplo, loophi, spmcrval storing and
; restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
;- It is assumed that the interrupts are disabled
.equ PAGESIZEB = PAGESIZE*2 ;PAGESIZEB is page size in BYTES, not words
.org SMALLBOOTSTART
Write_page:
; page erase
ldi spmcrval, (1<<PGERS) + (1<<SPMEN)
call Do_spm
; re-enable the Application Section
ldi spmcrval, (1<<ASRE) + (1<<SPMEN)
call Do_spm
; transfer data from RAM to Flash page buffer
ldi looplo, low(PAGESIZEB) ;init loop variable
ldi loophi, high(PAGESIZEB);not required for PAGESIZEB<=256
Wrloop:
ld r0, Y+
ld r1, Y+
ldi spmcrval, (1<<SPMEN)
call Do_spm
adiw ZH:ZL, 2