Roy,

Take a look at a program I wrote as a learning exercise that does something
simular to what you are trying to do.  It is a simulation of the old "magic
8 ball" that reads message strings from flash and displays them on an LCD.
The best example is one that outputs to the UART and is named 8BALLSIO.ASM
and is located at www.qsl.net/k5hj/avr along with a bunch of other small
programs I did in order to learn about the AVR.  Most are written for the
2313 but should apply to the MEGA parts as well.

Randy Ott

On Sat, 12 Jun 2004 09:07:25 +1200, Hopkins wrote
> Thanks again David -
>
> just one point I do not understand and that is how do you know the
> Table_Offset value or how do you know just were the table is located
> in memory?
>
> *************************************************
> Roy Hopkins   :-)
>
> Tauranga
> New Zealand
> *************************************************
> > >How do you program a lookup table in an AVR (ATMega 8) using assembler
> code?
> >
> > Assuming two regs named TEMP, TEMP2, and a ram var called Table_Offset
> with the pointer to the position in the table:
> >
> > Get_Table_Byte:
> >         ldi     TEMP,0                  ;For the 16 bit add to follow
> >         lds     TEMP2,Table_Offset      ;Get the offset
> >         ldi     ZL,low(Table*2)         ;Point at the table
> >         ldi     ZH,high(Table*2)        ;
> >         add     ZL,TEMP2                ;Add the offset as a 16 bit op
> >         adc     ZH,TEMP                 ;so the table can be anywhere.
> >         lpm     ;Defaults to R0, some AVRs can put it in other registers.
> >
> >         ret     ;Byte (Table offset) of TABLE is now in R0
> >
> > For reading multiple bytes, continue with
> >
> > adiw    ZL,1
> > lpm
> >
> > and so on.
> >
> > Data is stored in WORDS in the AVR rom, but recalled in BYTES.
> > Also, the assembler will append an extra null to the end of a .db that is
> an odd number of bytes long.
> >
> > TABLE: .db 0x45,0x46,0x47
> >
> > Ends up in rom as 45,46,47,00 << Extra null added by assembler.
> >
> > A table that ends in a null, like:
> >
> > TABLE: .db 0x45,0x46,0x43,0x47,0x00
> >
> > ends up looking like this: 45,46,43,47,00,00
> >
>
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