ChibiAkumas ASM Programming Forum

Hi.

Ok I finally understand what was the problem.

I thought that when we do "ld a, (&9000)", we assign the address &9000 to A, and any time we change the value of A, it is changed to the address &9000, as if A was a pointer.

So, this is already solved.

But now, I have one question: is it ...

Hi. Sorry for this next topic, but it is a bit unrelated to the other previous message.


Let's consider this piece of code, that appears in Lesson 3:

org &8000

ld a, (&9000)
ld bc, (&9001)

cp 0
jr z, MathAdd
cp 1
jr z, MathSub
ld a, 0

SaveResult:
ld a, (&9003)
ret

MathSub:
ld a, c
sub b
jr ...

Welcome to the forum, I'm glad you're finding my tutorials useful!

If you're looking to do some MSX assembly programming, can I strongly recommend you take a look at Grauw's website, as it's a wealth of MSX1/2 info

http://map.grauw.nl/resources/


Ah, yes, I know that website.
But for now, I ...

Hey there! this is CPC code isn't it...

in 8 bit systems when a register is 0 and we subtract 1 it 'rolls around' back to 255

I can't actually remember writing this example - I did it about 3 years ago, and maybe I'd do it differently today.

The example is going to repeat while A>=0 ... 255 is ...

Hi.

This piece of code:

ScreenSize equ &4000
org &8200
ld a, %00001111
FillAgain:
ld hl, &C000
ld de, &C000+1
ld bc, ScreenSize-1
ld (hl), a
ldir
dec a
cp 255
jp nz, FillAgain
ret

Just two questions:

1) In this specific example, I don't understand well how "CP" works and why we need it ...

Hi.

Thanks for your great content. I just found your website on the net.
I want to write software for the MSX 1 and your lessons are maybe the best around, for people who are new to assembly language.

I know how to code in C/C++, BASIC, LUA and TCL/TK. Now trying to get things done they way they ...