ATMEGA48V_11 ATMEL [ATMEL Corporation], ATMEGA48V_11 Datasheet - Page 265

• Manufacturer Part Number: ATMEGA48V_11
• Description: 8-bit Atmel Microcontroller with 4/8/16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

26.2.4
26.2.5
2545T–AVR–05/11
Programming time for flash when using SPM
Simple assembly code example for a boot loader
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. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
2. 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 26-1.
Note:
Note that the RWWSB bit will always be read as zero in Atmel ATmega48. Nevertheless, it is
recommended to check this bit as shown in the code example, to ensure compatibility with
devices supporting Read-While-Write.
Flash write (page erase, page
write, and write lock bits by SPM)
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.
.equ PAGESIZEB = PAGESIZE*2
.org SMALLBOOTSTART
Write_page:
;-the routine writes one page of data from RAM to Flash
; the first data location in RAM is pointed to by the Y pointer
; the first data location in Flash is pointed to by the Z-pointer
;-error handling is not included
;-the routine must be placed inside the Boot space
; (at least the Do_spm sub routine). Only code inside NRWW section can
; be read during Self-Programming (Page Erase and Page Write).
;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),
; loophi (r25), spmcrval (r20)
; 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 either the interrupt table is moved to the Boot
; loader section or that the interrupts are disabled.
; Page Erase
ldi
rcallDo_spm
; re-enable the RWW section
ldi
1. Minimum and maximum programming time is per individual operation.
spmcrval, (1<<PGERS) | (1<<SELFPRGEN)
spmcrval, (1<<RWWSRE) | (1<<SELFPRGEN)
Symbol
SPM programming time
Minimum programming time
(1)
.
;PAGESIZEB is page size in BYTES, not words
3.7ms
CC
Table 27-5 on page 279
ATmega48/88/168
reset protection circuit can be
Maximum programming time
CC
. This will pre-
4.5ms
shows the
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