From: Ed Beroset 
Subject: Re: Directly writing to memor
At 20:28 1/28/98, you wrote:
>
> *** Darryl Gregorash wrote in a message to Scott McNay:
>
> DG>> mov ss:[sp], eax
> DG>> sub sp,4
>
>
> SM> Shouldn't that be the other way around?
>
>DG> I don't think so; it mimics a PUSH.
>
>Last I heard, SP pointed at the top of the stack, so that SS:[SP] would 
efer
>to the last item.  Meaning, to add another value to the stack, you must 
irst
>decrement sp, then move the new value, as in:
>
>  sub sp,4
>  mov ss:[sp],eax
You're correct.  The stack pointer is decremented before the register is
copied to memory.  
> SM> (assuming, of course, that mov ax,ss:[sp] worked ;)
>
>DG> Why wouldn't it?
>
>Did you try it?  Microsoft's DEBUG says "error", and OpenDOS's DEBUG says
>"Incorrect name of index register".
That's because it's not a legal addressing mode.  If you examine a chart of
the  ModR/M byte addressing forms, you'll see that there is no way to
specify [sp] as a destination address.
Ed
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