Just curious - why are you using switches instead of a micro ?
Is it a 60s revival thing ?

> Another Q... I guess CG stands for character generator, but
> why is there an operation to write to CG RAM?  What's the
> purpose of that?  Can I create my own fonts or something?

Yes, there are normally 8 characters (ASCII 00 to 07) that can
be drawn with your own data. For example I use this set of data
to define 00 as a +/- sign

         movlw   0x40         ;set LCD address to CG 00
         call    write_c         ;write command
         clrf   temp              ;byte address and counter

getbyte  movlw   0x04  ;get data
              movwf   pclath
         movf    temp,w
         call    pmsign

         call    write_d       ;write it to LCD

         incf    temp,f
         movlw   0x08       ;count 8
         xorwf   temp,w
         btfss   status,z
         goto    getbyte    ;loop

=========================

 org 0x400

pmsign   addwf   pcl,f        ;redefine char 00 as +/-
         retlw   0x04
         retlw   0x04
         retlw   0x1f
         retlw   0x04
         retlw   0x04
         retlw   0x00
         retlw   0x1f
         retlw   0x00

The CG RAM can also be used as general purpose storage RAM
for the micro btw

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