Compile learning notes for beginners (4) -- [BX] and loop commands

Getting started with crazy summer vacation Study Notes (4) -- [BX] and loop commands

Reference: Chapter 5th of Assembly Language

1. [BX]

MoV Al, [1]

In debug, data in BS: 1 is assigned to Al, but data in BS: 1 is not assigned to Al in MASM, instead, [1] is considered to be 1 assigned to Al.

If you want to implement mov Al, [1] In debug, you need [BX] In MASM.

For example:

MoV BX, 1

MoV Al, [BX]

You can also use BS: [1 ].

For example:

MoV Al, BS: [1]

2. Loop

Loop command should be used for Loop

Example: Calculate 2 ^ 20

assume cs:codesgcodesg segmentstart:mov ax,0mov cx,20s:add ax,2loop smov ax,4c00Hint 21Hcodesg endsend start

The number of times that CX stores loops. Each cycle minus 1

S indicates the start of the loop. The loop jumps to S. You can use DEBUG to debug the code above. Loop S is actually loop 0006 H.

3. Loop debugging in debug

You can run-G 000b (install the above Code for debugging) to stop the specified code to exit the loop.

Or use-P directly in the loop to jump out of the loop.

4. A security space

In general, 0: 200h ~ in DOS ~ 0: The 2ffh space does not have data or code of the system or other programs. It can be used.

5. Use of segment prefix

MoV Al, BS: [1]

BS: the segment prefix.

Not only BS can

MoV ax, DS: [BX]

MoV ax, CS: [BX]

MoV ax, SS: [BX]

MoV ax, ES: [BX]

Yes

Example: Put the memory FFFF: 0 ~ FFFF: Copy Data in Unit B ~ 020: f.

assume cs:codesgcodesg segmentstart:mov ax,0ffffhmov ds,axmov ax,0020Hmov es,axmov cx,12mov bx,0s:mov al,ds:[bx]mov es:[bx],alinc bxloop smov ax,4c00Hint 21Hcodesg endsend start