Ricardo,

I've run into this same problem, which is that constants defined
in one .asm file (with the #define directive) cannot be declared
GLOBAL as can be done with variables.

The solution I arrived at was to #define bit assignments and
other global constants in a separate "global declarations" file,
and then #include that file at the beginning of each .asm file of
the project.  The global declarations file also contains the
#include directive which brings in Microchip's processor
definitions file (for instance, p16f877.inc).

That way, I can change bit assignments, and even the target
device for a project, by editing only one file instead of editing
every .asm source file.

Hope this helps a bit...

Dave D.

Ricardo Medina wrote...

>I am trying my hand at relocatable code (using assembler for 16F628 and
>16F877 parts), but I fell into a bit of a blind hole...
>
>The project worked perfectly the first time out (which I must admit is quite
>strange, as it is my first attempt at driving anything more complex than a
>transistor...), and it is basically a PIC writing a message to a 16x2
>character LCD display.
>
>The code is structured in three files:
>delay.o -> contains various delay subs, which are totally independent from
>the main program
>lcd.o     -> contains the LCD subs
>main.o   -> contains the main program flow, what I want to display, etc.
>
>At first I statically set the port and bits to control the LCD inside lcd.o,
>but afterwards I decided that the whole point of using relocatable code is
>to be able to port it to other projects as easily as possible... So, from
>then on, I used six variables in the lcd.o object file which would be
>defined in the main.o file. (the idea behind this is to be able to change
>the ports and bits used by the LCD, depending on the complexity or needs of
>the project.)
>
>So I defined:
>LCTRL -> The port which has the LCD control lines (RS, RW, EN)
>LBUS   -> The port which holds the LCD data/address
>LBUST -> LBUS direction control (LBUS's TRIS register)
>RS -> Bit n: for the RS line
>RW -> Bit n: for the RW line
>EN -> Bit n: for the EN line.
>
>The problem is that I can assign the registers in main.o, but not the bits!!
>For example:
>LPORTS  UDATA   0x05
>LCTRL    RES    1    ; Set LCTRL as PORTA
>LBUS    RES    1      ; Set LBUS as PORTB
>
>LTRIS    UDATA    0x86
>LBUST    RES    1    ; Set LBUST as TRISB
>
>and afterwards I set them global.... no problem there.... but I still
>haven't found a way to specify the three control bits in the main file, and
>getting them to be global!
>
>Can anyone give me a clue, or is the only way to do it to use a mask (like,
>if I want EN to be bit 2, I set a register as EN and I set it's 2nd bit, so
>if I want to  " bsf LCTRL,EN " instead I do:
>
>movlw 0xFF
>andwf    EN,W
>iorwf    LCTRL
>
>That would eventually get the job done, but it's 3 times as long, and not
>very "neat", shall we say, right?
>
>I'm very sorry to take up your time, but I couldn't find the answer
>anywhere, and I've been at this for about three days, trying all the
>different combinations I could think of... If anyone can shed some light,
>I'd greatly appreciate it.
>
>Thank you all very much,
>
>Ricardo Medina

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