"OUT" Instruction 
Author Message
 "OUT" Instruction

Hi There All

I am a newbie to disassembling the 80x86 based stuff and this is my
first posting on the subject.

I hoping that someone out there can shed some light on the following:-

I am trying to disassmble the bios on my laptop using Borlands TD
which seems to be ok and coping ok with the Instruction set (appearing
80486 based).

There is a point in the bios code that carrys out an "OUT &HB2,AL"

Now correct me if I am wrong but all the literature on the "out"
instruction suggests that it has no effect on any of the registers
such as AX and BX, yet when I step through this instruction, it
appears the change the AX and BX registers upon completion of this
instruction.

Now my thoughts are leading me to beleive that the "out" intruction is
causing some sort of hardware interupt that TurboDebbug cannot follow
and hence causing the processor to run some code that potentially
manipulates these registers AX & BX, accounting for there sudden value
changes.

Now my questions are as follows:-

Is there any credance in what I just said or is it all a load of
twoddle and I am missing something completely obvious.

And

If what I just said is probably along the right lines how do I suss
out where the hardware interupt table would be in order to try and
trace the vector.

Regards

Mark



Sun, 25 Jul 2004 03:24:59 GMT  
 
 [ 1 post ] 

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