I know this is available on many PIC enthusiast sites, and it is also in an
app note on the Microchip site, but it is so simple that I'll state it
here.

Starting with the lookup value in W, call a lookup subroutine to get the
converted value, also in W.

convert:
    addwf PCL,1
    retlw val 1    ; W = 0
    retlw val 2    ; W = 1
    retlw val 3    ; W = 2
    retlw val 4    ; W = 3
    retlw val 5    ; W = 4
    ...
    retlw val n    ; W = n-1

Note that the entire lookup table must not cross a page boundary.  This all
depends on the unusual fact (compared to other MCU's) that the PIC program
counter can be manipulated like any other register by the addwf
instruction.


HTH - Martin R. Green
elimar@bigfoot.com


----------
From:   Steven J Tucker[SMTP:classics@NACS.NET]
Sent:   Friday, September 19, 1997 12:44 AM
To:     PICLIST@mitvma.mit.edu
Subject:        Re: PIC or SBC?

On Thu, 18 Sep 1997, Martin R. Green wrote:

> The current issue of Steve Ciarcia's Circuit Cellar Ink magazine has a
> project almost identical to what you are doing, except it converts PC

[snip]

Thanks for the info, I will look for it.

> PPS.  If you use a PIC, you don't need to EEPROM for the conversion
tables,
> you should be able to use RETLW ROM lookup tables instead.

Can you point me to any examples of this?  I assume you mean a large
 block of RETLW statements, w/ an indirect CALL somehow?  On a 6502 there
 is an indirect JSR addressing mode, but on the pic?  I would really love
 to see how this is done, seems very inventive :)

Steve

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