Hi list,

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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