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Index > DOS > MOVing register into RAM, DOS

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jatos



Joined: 04 Nov 2006
Posts: 20
jatos
I know this may well have been asked before, but I have searched on the forums.

I know I can use MOV to move the contents of a register directly into the memory with anything PUSH or POP. However, how I do know in DOS which memory address to give to MOV?

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Jamie
Post 15 Mar 2007, 14:38
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eek



Joined: 21 Oct 2006
Posts: 24
eek
use the ketman interpreter to get a picture for what you're doing.

http://www.btinternet.com/~btketman/tutpage.html

While it isn't FASM and is only 16bit it WILL save you asking a few thousand questions.

A push puts the value onto the stack.
Other areas of memory can be reserved for values of different size or even dynamic values.
Post 15 Mar 2007, 21:36
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rugxulo



Joined: 09 Aug 2005
Posts: 2341
Location: Usono (aka, USA)
rugxulo
Try using GRDB (DOS debugger, but works under Win XP) to view registers before and after instructions. It also allows immediate execution of instructions directly (/and ax,127) without having to assemble and run. It supports at least up through MMX, if not more by now (I forget).
Post 16 Mar 2007, 03:38
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DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
Quote:
but works under Win XP


Sad


Quote:
how I do know in DOS which memory address to give to MOV?


Code:
--------D-2148-------------------------------
INT 21 - DOS 2+ - ALLOCATE MEMORY
        AH = 48h
        BX = number of paragraphs to allocate
Return: CF clear if successful
            AX = segment of allocated block
        CF set on error
            AX = error code (07h,08h) (see #01680 at AH=59h/BX=0000h)
            BX = size of largest available block
Notes:  DOS 2.1-6.0 coalesces free blocks while scanning for a block to
          allocate
        .COM programs are initially allocated the largest available memory
          block, and should free some memory with AH=49h before attempting any
          allocations
        under the FlashTek X-32 DOS extender, EBX contains a protected-mode
          near pointer to the allocated block on a successful return
SeeAlso: AH=49h,AH=4Ah,AH=58h,AH=83h
--------D-2149-------------------------------
INT 21 - DOS 2+ - FREE MEMORY
        AH = 49h
        ES = segment of block to free
Return: CF clear if successful
        CF set on error
            AX = error code (07h,09h) (see #01680 at AH=59h/BX=0000h)
Notes:  apparently never returns an error 07h, despite official docs; DOS 2.1+
          code contains only an error 09h exit
        DOS 2.1-6.0 does not coalesce adjacent free blocks when a block is
          freed, only when a block is allocated or resized
        the code for this function is identical in DOS 2.1-6.0 except for
          calls to start/end a critical section in DOS 3.0+
SeeAlso: AH=48h,AH=4Ah
--------D-214A-------------------------------
INT 21 - DOS 2+ - RESIZE MEMORY BLOCK
        AH = 4Ah
        BX = new size in paragraphs
        ES = segment of block to resize
Return: CF clear if successful
        CF set on error
            AX = error code (07h,08h,09h) (see #01680 at AH=59h/BX=0000h)
            BX = maximum paragraphs available for specified memory block
Notes:  under DOS 2.1-6.0, if there is insufficient memory to expand the block
          as much as requested, the block will be made as large as possible
        DOS 2.1-6.0 coalesces any free blocks immediately following the block
          to be resized
SeeAlso: AH=48h,AH=49h,AH=83h
    


You can also reserve memory just above your executable, see:

http://board.flatassembler.net/topic.php?t=6735 (In Main, MZ examples)

_________________
Bug Nr.: 12345

Title: Hello World program compiles to 100 KB !!!

Status: Closed: NOT a Bug
Post 17 Mar 2007, 05:09
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rugxulo



Joined: 09 Aug 2005
Posts: 2341
Location: Usono (aka, USA)
rugxulo
Quote:

but works under Win XP Sad


It works under DOS and Win XP (unlike 386SWAT, loaded as a device driver, which needs DOS or QEMU or whatever ...).
Post 29 Mar 2007, 00:33
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