Thanks for the fast response - will test it out.

----- Original Message -----
From: "David VanHorn" <dvanhorn@CEDAR.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, June 11, 2004 7:58 PM
Subject: Re: [AVR:]Look up Table


> At 07:32 PM 6/11/2004 +1200, Hopkins wrote:
>
> >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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