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Well, today we're learning about a very
important element in any ASM program, or in ANY program that is. We're
learning about display functions. First, I'll be talking a little about
labels again, just to refresh you, and then I'll be getting into text display
RECAP ON LABELS
Now, I hope you remember how to use labels.
If not, here's a small reminder:
Lables work the same way in ASM as they
do in BASIC, except for the way you 'Goto' them. Labels in ASM require
a 'jp' command. If you forgot about the 'jp' command, I suggest you read
my previous logs, or just pretend you know and continue.
Now that was short, wasn't it? That should
be all you need to know, because I am going to tell you of a new way to
call labels. first, I'll show you a simple load command:
This loads the number 5 into 'a', right?
Good. Now, here is a little more complicated rutine (or command, I'll refer
to them as either):
I effect, if the accumulator, or 'a', were
set to 5 as stated above, this will load 'a', or 5, into the variable '(currow)'.
"What is (currow), Phil?" you ask? Well, on the home screen,
each letter or number takes up one block. You can fit 8 of these blocks
along the side of the screen, going down, right? This means there are 8
rows on the home screen, or the "cursor" screen. CURsor ROW.
CURROW. '(currow)', get it? Now that the '(currow)' is set to 5, the cursor
will move there, ready to print something.
Here's another load rutine:
You might be asking, "Phil, I know
what '(currow)' is now, but what is '(curcol)'?" Well, it is very
similer to '(currow)'. If you were looking at the home screen, or cursor
screen, you will see that you can fit 16 numbers or letters (or symbols)
in a row. This means that there are 16 columns on the cursor screen. CURsor
COLumn. CURCOL. '(curcol)', get it? Good.
Now we have selected the cursor to be at
(5,6). On the 83, that would look like this:
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
« - - - - - - - - - - - - - - - - »
« - - - - - - - - - - - - - - - - »
Now that's pretty easy to understand if
you know how to use BASIC's 'Output(' command. The problem is, if you use
BASIC's 'Output(' command like this...
...you will get an error. What you need
is something to say, something to write on the screen. That's where labels
Now, the command that you would use to
display (I'll talk about it later) needs an input of '(currow)', '(curcol)',
and 'hl', kind of like how 'Output(' needs a X coordinate, a Y coordinate,
and a string to output. If you wanted to do this in basic...
...you would need to define 'Str1' somewhere
in the program before this point. In ASM, though, you can define strings
anywhere you want to in the program, because the program treats them as
I want my program to say "Hi there!",
so I need someway a getting that into 'hl'. Here's how. I would first make
a label called, oh lets call it 'STRING_ONE' for the hell of it. This is
Now, I need to write the string. The command
for doing this is '.db'. I don't know, what '.db' stands for, and I don't
really care as long as it gets the job done. Anything after '.db' on a
line is considered a string. So I'll put my string in.
.db "Hi there!"
The only thing is, you have to tell the
program when the string is over. To do so, just add a comma and a 0 after
.db "Hi there!",0
(If you can't make it out, that's a zero,
not an "oh")
Now, I need to get all of this into 'hl'.
This is really easy. All I have to do is load the label into the variable,
and viola! This is done like so:
"Now I'm done, right Phil?" Nope.
There's one more thing that has to be done. You have the X variable, the
Y variable, and the string, but I haven't told you the command to display
the message on the screen yet. The command is '_puts', and you have to
call it like '_clrLCDFull'. As a little hint, all commands that start with
an underscore are required to be called, with the 'call' command. Here's
Alright. We have the X variable, the Y
variable, the String, and we've displayed the string on the screen. The
program is complete. Here, now, for you to view, is the entire program
from start to finish. I will add some notes to the source too, just so
you can understand each line.
.NOLIST ;You ought to know what this is by now.
#define equ .equ
#define EQU .equ
#define end .end
call _clrLCDFull ;Clear the screen
ld a,5 ;load 5 into acc.
ld (currow),a ;load acc. (5) into (currow)
ld a,6 ;load 6 into acc.
ld (curcol),a ;load acc. (6) into (curcol)
ld hl,STRING_ONE ;load string STRING_ONE into hl
call _puts ;displays
ret ;returns to origional program
STRING_ONE: ;Label STRING_ONE follows
.db "Hi there!",0 ;defines string as "Hi there!"
end ;ends program
Cool. Now assemble it as I told you in
the first volume, and have a great time. Change the location of the text!
Change the message! Whoopee!
Thanks just about everyone. If you've read
the others, you know em' pretty well by now.
Thanks for your time, and I'll see you in the ASM Log 5! -Phil