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Index > DOS > PUSH -> "clear" code doesn't work

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dieboy



Joined: 30 Dec 2004
Posts: 41
Location: Poland, Elblag
dieboy
Hello!
Code:
push ax
;is like :
sub sp, 2
mov ss:[sp], ax
;but in TASM    

and how to write this code in FASM? if I write ... [ss:sp] i have an error. Can you tell me ?

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Post 18 May 2005, 18:37
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YONG



Joined: 16 Mar 2005
Posts: 8000
Location: 22° 15' N | 114° 10' E
YONG
Try this:
Code:
                sub     sp, 2
                mov     bp, sp
                mov     [bp], ax
    


Your error was not related to ss. It was about [sp] which is illegal.

Listed below are the legal 16-bit Memory Addressing Modes:
- Displacement
- bx or bp
- si or di
- Any combinations of the above three

YONG
Post 18 May 2005, 19:45
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mike.dld



Joined: 03 Oct 2003
Posts: 235
Location: Belarus, Minsk
mike.dld
In 16-bit code there is no SP-relative addressing (only BP,BX,SI,DI can be used). But you can probably write
Code:
sub sp, 2
mov [esp], ax     
Post 18 May 2005, 19:53
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YONG



Joined: 16 Mar 2005
Posts: 8000
Location: 22° 15' N | 114° 10' E
YONG
One more point.

Even though the [bp] addressing mode uses ss by default,
you may code [ss:bp] to make it clear and unambiguous.

YONG
Post 18 May 2005, 20:21
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MazeGen



Joined: 06 Oct 2003
Posts: 975
Location: Czechoslovakia
MazeGen
mike.dld wrote:
In 16-bit code there is no SP-relative addressing (only BP,BX,SI,DI can be used). But you can probably write
Code:
sub sp, 2
mov [esp], ax     

You can never be sure that high word of ESP is zero, so MOVZX ESP,SP should be used before such code.

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Post 18 May 2005, 20:59
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dieboy



Joined: 30 Dec 2004
Posts: 41
Location: Poland, Elblag
dieboy
Ok. Thank you very much! Smile

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Post 19 May 2005, 06:15
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