On Tue, Mar 03, 1998 at 07:04:35PM -0400, Bob Smith x31105 wrote:

> for this beasty leaves me with the belief that I can't use ROM address
> space for data?!?!  somebody tell me I'm blind and haven't read the
> correct page!

You're very nearly right; data tables on a mid-range PIC are implemented
as RETLW tables, indexed by an addwf PCL. For example:

table     addwf   pcl
          retlw   1
          retlw   2

You access the data with a call, with the 8 bit index of the data you want
in W. You also have to worry about ROM pages if you have more than 2K
of ROM. This technique stores 8 bits of data per 14 bit instruction.

the same applies on the baseline PICs (12 bits instead of 14) but
the high-end have instructions to read (and write!) the external program
memory space.

--
Clyde Smith-Stubbs               |            HI-TECH Software
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