Variables, Labels, Loops

[Munchor]

I have this code (in Mimas):

Code: [Select]

Start:
  db $ef,$40,$45
  ld b,100
  ld a,0
Loop:
  add a,myNum
  djnz Loop
  ld l,a
  db $21,$01,$00
  db $ef,$07,$45
  B_CALL (_GetKey)  ;ef4972
  ret
myNum:
  db 3

I'm trying to make a loop where I add 3 to a 100 times.

Will this ever work? I'm not sure if I can set variables like that or only by (myVar .equ 3).

Thanks.

[aeTIos]

Mimas=cool, huh?
You'll get 300-255=a 45 higher than the offset because the registers are 8-bits. I think this will work, you just should try it out.

[Munchor]

aeTIos: That's not the problem, this won't work too, I think:

Code: [Select]

Start:
  db $ef,$40,$45
  ld b,100
  ld a,0
Loop:
  add a,myNum
  djnz Loop
  ld l,a
  db $21,$01,$00
  db $ef,$07,$45
  B_CALL (_GetKey)  ;ef4972
  ret
myNum:
  db 1

[Deep Toaster]

myNum isn't 1; it's a pointer to a byte that's one. In other words, you're adding something like 40,371 to A every pass.

EDIT: Quick explanation of pointers here if you're confused

[ZippyDee]

You need to do add a,(myNum)

myNum is merely labeling the address at which the data is found. You then have to indirectly load the data from the address.

[Deep Toaster]

I don't think ADD A,(n) is valid...

You'll have to do LD HL,myNum \ ADD A,(HL).

[ZippyDee]

Ah yes, you're right. My bad.

[ralphdspam]

You can use ld a,(Address) instead of loading the address to HL first.

[thepenguin77]

Just a question. Why are you doing in-line assembly in assembly? Why not just type out the bcall? It makes it easier for the non-xeda's to read

[ralphdspam]

Also, if you want to do multiplication (I think that is what you want), you can use one of these routines:
http://wikiti.brandonw.net/index.php?title=Z80_Routines:Math:Multiplication

[Munchor]

Just a question. Why are you doing in-line assembly in assembly? Why not just type out the bcall? It makes it easier for the non-xeda's to read

But easier for me to code, sorry.

add a,(mynum) Thanks, I actually though stuff inside parentheses were adresses and without parentheses were values. Is it different for variables??

[Deep Toaster]

You can use ld a,(Address) instead of loading the address to HL first.

It needs to be added to A, though.

add a,(mynum)

See my post above -- ADD A,(n) isn't valid.

Thanks, I actually though stuff inside parentheses were adresses and without parentheses were values. Is it different for variables??

That's exactly it. myNum is a pointer that points to a byte that has a value of 3.

I don't think you understand what "variables" are in ASM. In ASM, a "variable" is just a byte (or two bytes) of data reserved for a purpose. In this case, you use .db to reserve a byte that has a value of 3, and you label it as myNum -- the pointer of that byte.

[Ashbad]

This should work:

Code: [Select]

   XOR A
   LD H,0
   LD B,100
Loop
   INC  A
   DJNZ Loop
End
   LD L,A
   RST 28h
   .dw DispHL
   RET
This assumes that since MyVar is one, it can just use an increment sequence instead
   

[Munchor]

You can use ld a,(Address) instead of loading the address to HL first.

It needs to be added to A, though.

add a,(mynum)

See my post above -- ADD A,(n) isn't valid.

Thanks, I actually though stuff inside parentheses were adresses and without parentheses were values. Is it different for variables??

That's exactly it. myNum is a pointer that points to a byte that has a value of 3.

I don't think you understand what "variables" are in ASM. In ASM, a "variable" is just a byte (or two bytes) of data reserved for a purpose. In this case, you use .db to reserve a byte that has a value of 3, and you label it as myNum -- the pointer of that byte.

That explained it all, thanks a lot.