ATmega16 datasheet(250/315 Pages) ATMEL

250 / 315 page

250

ATmega16(L)

2466E–AVR–10/02

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):

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.

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

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.

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 SPMCR register and thus the Flash from unintentional

writes.

Programming Time for Flash

when using SPM

The Calibrated RC Oscillator is used to time Flash accesses. Table 98 shows the typical

programming time for Flash accesses from the CPU.

Simple 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

; 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.

.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 RWW section

ldi

spmcrval, (1<<RWWSRE) | (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:

r0, Y+

r1, Y+

ldi

spmcrval, (1<<SPMEN)

Table 98. SPM Programming Time.

Symbol

Min Programming Time

Max Programming Time

Flash write (Page Erase, Page

Write, and write Lock bits by SPM)

3.7 ms

4.5 ms

ATMEGA16 Datasheet(PDF) 250 Page - ATMEL Corporation

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