Alright I agree I am a pure noob in ASM,
When I try this code it says "Invalid Operand Address","Invalid Operand"

What I wanted to simply do is assign the value of DH + 1, to DL,
Note: DH needs to be preserved before calling the function, so I can't use :

lol I know this is one of the WORST questions EVER!
But I can't get my code work![/code]

Everything closed in square brackets is address. But x86 can't use 8bit registers as address. You need to Note that if it was 32bit register you could do: because 32bit addresses are valid.

Why didn't I think about that? That's common sense. I guess my question was pretty lame. Thanks!

A useful reference is http://ref.x86asm.net/coder32-abc.html#modrm_byte_16 which shows the valid effective addresses in 16bit; note that the only registers you can use are bx/si/di/bp. (This is somethign that gets me every time I change my boot loader because I'm used to 64bit code )

Helpful are the instructions

MOVZX
MOVSX

as well. MOVZX will clear the upper part of a register when transferring the lower part.

Like MOVZX CX,DL which is a combination of

XOR CX,CX
MOV CL,DL

Not precisely because MOVZX does not alter the flags, whereas XOR does.

Okay, lets write:

MOV CH,0
MOV CL,DL

Also I have one more question, How would I do this :
MOV SI,AL?