> I'm sure this has come up before, but is there a way
> to store and read numerical data from the program
> memory of the 16F84?

Most of the F series parts can read and write their own program memory via
the same EECON interface used to access the data EEPROM.  I don't know about
the 16F84 specifically, but I've done this on the F876 and F877.

The alternate way of storing data in program memory is a table of RETLW
instructions.

> I've been working on a "Propeller
> Clock" and while there is enough memory to store
> numbers in the EEPROM I wouldn't mind being able to
> store letters for the days of the week if possible
> (without having some sort of add-on memory chip).

I've done a similar thing on a 16C66 driving a rotating LED display.  Most
of the program memory is RETLW instructions that implement a font table for
the 256 possible characters.

By the way, it helps to have a font "compiler" that translates a pictorial
representation of the character to the format most convenient to the
firmware.  You'll go nuts trying to fill in the right 1s and 0s in the font
table if you try to do more than a few characters.  For example, here's a
snippet of my font "source" code:

char 65 "A"

- - * * * * * - - -
- * * * * * * * - -
* * * - - - * * * -
* * - - - - - * * -
* * - - - - - * * -
* * * * * * * * * -
* * * * * * * * * -
* * - - - - - * * -
* * - - - - - * * -
* * - - - - - * * -
* * - - - - - * * -
* * - - - - - * * -
* * - - - - - * * -
- - - - - - - - - -
- - - - - - - - - -
- - - - - - - - - -

And here is a snippet of the assembly source that is automatically generated
from the font above:

;
;   Char 65 "A"
;
         retlw   b'00011111'
         retlw   b'11111100'
         retlw   b'00011111'
         retlw   b'11111110'
         retlw   b'00000000'
         retlw   b'01100111'
         retlw   b'00000000'
         retlw   b'01100011'
         retlw   b'00000000'
         retlw   b'01100011'
         retlw   b'00000000'
         retlw   b'01100011'
         retlw   b'00000000'
         retlw   b'01100111'
         retlw   b'00011111'
         retlw   b'11111110'
         retlw   b'00011111'
         retlw   b'11111100'
         retlw   b'00000000'
         retlw   b'00000000'


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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