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Z80 & 68k Assembly =>
z80 & ez80 Assembly
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Exfyre
Newbie
Joined: 10 Jun 2009
Posts: 8
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 Posted: 21 Jun 2009 10:46:36 am Post subject: |
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Code:
#include "ti83plus.inc"
#define bcall(label) RST 28h \ .dw label
.org $9D93
.db $BB,$6D
start:
b_call(_ClrLCDFull)
b_call(_HomeUp)
ld hl, text1
push hl
ld a,0
ld b,10
loop1:
pop hl
b_call(_PutS)
push hl
dec b
cp b
jr z,loop1
ret
text1:
.db "* *"
.db "* *"
.db "* *"
.end
END
I want this to loop through loop1 label ten times, but instead, it loops through the whole program an infinite number of times. What have I done wrong? |
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simplethinker
snjwffl
Active Member
Joined: 25 Jul 2006
Posts: 700
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| Posted: 21 Jun 2009 11:25:52 am Post subject: |
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Code:
loop1:
pop hl
b_call(_PutS)
push hl
dec b
cp b
jr z,loop1
ret
You want it to not jump back when the B register is zero, which means you want it to jump when the B register is not zero. If you change "jr z, loop1" to "jr nz, loop1" this should fix your problem.
There are a couple other things that could be changed/simplified:
1) "dec B" will affect the flags, so you don't need the "cp B". This also means you can eliminate the "ld A, 0" part since it's only there for the compare with B.
2) There's an instruction "djnz label" ("djnz" stands for Decrement and Jump if Not Zero) that will decrease B and, if B is not zero, jump to "label". This is essentially equivalent to:
Code:
dec B
jp nz, label
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Exfyre
Newbie
Joined: 10 Jun 2009
Posts: 8
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| Posted: 21 Jun 2009 11:52:56 am Post subject: |
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Ok, I changed the code to this:
Code:
#include "ti83plus.inc"
#define bcall(label) RST 28h \ .dw label
.org $9D93
.db $BB,$6D
start:
b_call(_ClrLCDFull)
b_call(_HomeUp)
ld hl, text1
push hl
ld a,0
ld b,10
loop1:
pop hl
b_call(_PutS)
push hl
djnz loop1
ret
text1:
.db "* *"
.db "* *"
.db "* *"
.end
END
However, the calculator still loops infinitely through the whole program.
EDIT:
I found out what the problem was. I'd had pops and pushes in the wrong places. I'm guessing _PutS destroyed register b? (lemme know if I'm wrong)
fixed code:
Code:
#include "ti83plus.inc"
#define bcall(label) RST 28h \ .dw label
.org $9D93
.db $BB,$6D
start:
b_call(_ClrLCDFull)
b_call(_HomeUp)
ld hl, text1
ld b,10
loop1:
push bc
push hl
b_call(_PutS)
pop hl
pop bc
djnz loop1
ret
text1:
.db "* *"
.end
END
Last edited by Guest on 21 Jun 2009 12:09:09 pm; edited 1 time in total |
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simplethinker
snjwffl
Active Member
Joined: 25 Jul 2006
Posts: 700
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| Posted: 21 Jun 2009 12:29:54 pm Post subject: |
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[s]I don't think that _PutS modifies B (my list of routines says it only modifies HL), but if that fixes the problem, then that's probably the problem.[/s]
[edit] Your problem is the string you're using. _PutS need a zero-terminated string, so you'll need
Code:
.db "* *", 0
to be your string. Othewise, _PutS will print characters until it eventually runs into a 00 (which could be pretty much anywhere).
Last edited by Guest on 21 Jun 2009 12:32:17 pm; edited 1 time in total |
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Exfyre
Newbie
Joined: 10 Jun 2009
Posts: 8
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| Posted: 21 Jun 2009 12:31:35 pm Post subject: |
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| then hl must have been the problem, because in the original code i popped HL before the PutS and pushed it after, saving the altered version.. |
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cjgone
Aw3s0m3
Active Member
Joined: 24 May 2006
Posts: 693
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| Posted: 23 Jun 2009 12:33:56 pm Post subject: |
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Null terminated string error and I think PutS destroys B, so yes, you have to save it.
exfyre wrote: then hl must have been the problem, because in the original code i popped HL before the PutS and pushed it after, saving the altered version..
I don't quite understand what you're trying to say. Best to push hl at the start of the loop and pop it before re-looping. It might be even faster to just do "ld hl,text1" instead of a push\pop.
Last edited by Guest on 23 Jun 2009 12:36:26 pm; edited 1 time in total |
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simplethinker
snjwffl
Active Member
Joined: 25 Jul 2006
Posts: 700
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| Posted: 23 Jun 2009 03:20:18 pm Post subject: |
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cjgone wrote: Null terminated string error and I think PutS destroys B, so yes, you have to save it.
PutS doesn't destroy B.
Code:
ld B, 8
_testLoop:
ld HL, text
b_call(_PutS)
djnz _testLoop
ret
text:
.db "H", $00
works fine. |
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cjgone
Aw3s0m3
Active Member
Joined: 24 May 2006
Posts: 693
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| Posted: 24 Jun 2009 01:33:12 pm Post subject: |
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| Yea my bad. I forgot what PuTs destroys. |
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