Substraction...
 

Hi how can i substract value1 from EAX.
value1 = 0FFFFh.

MOV eax,value1
sub eax,value1

Is that correct?

It appears to be correct

I would suggest that you could just set EAX to zero. However, if you want to subtract value1 from another value, then put the other value in EAX and subtract value1.

So is right:
mov eax,value1
sub eax,value1

I know what you are saying:
mov eax,0. but this is what the Mr. want me to do. thanks DaWei.

If you subtract a value from itself, you will get zero. At least, it used to be that way. I won't address possible glitches arising from twos-complement usage.