Assembly language--register (Memory access DS data segment register, SS stack segment register)

Storage of words in memory

The main meaning of this passage is: a word =2b=16bit,the CPU is a two memory units stored in a word (if the 0 address to store the font data, is to get its high-byte 0+1 bit and low byte 0 bits data, the data is read by the high address bit to the low address bit)

Questions:

(1) What is the byte-type data stored in the 0 address unit? # 20H
(2) What is the font data stored in the 0 address word cell? # 4e20h
(3) What is the byte-type data stored in the 2 address word cell? # 12H
(4) What is the font data stored in the 2 address unit? # 0012H
(5) What is the font data stored in the 1 address word cell? # 12aEH

Conclusion: As I said above, the font data is the data of it and its next address unit (the data is read from the high address bit to the low address bit)

Data Segment Register DS and offset [address]

Usage is similar to CS and IP, and is the value of the segment register Value *16+ offset

To the DS data segment register Value

Because the CPU segment registers are shy, they cannot be assigned directly (the CS Code register is in jmp Cs:ip), so the segment registers are assigned in the following way

MOV ax,1234h    # assigns AX register to 1234Hmov ds,ax    # Indirect assignment via AX register

Transmission of Word

mov ax,[1]    # [] is offset meaning to assign 12341 memory location Glyph data to AX Register mov al,[1]    # assigns byte-shaped data from 12341 memory locations to Al (Low) Register mov  [1],ax # to assign    AX register glyph data to a value of 12341 memory location mov [1],al    # assigns the byte-shape data of the Al register to the 12341 memory location

Question 1:

In memory, for example, write out the following instruction after the execution of the value in the Register AX,BX,CX?

parsing:

Question 2:

In memory, for example, write out the following instruction after the execution of the value in the Register AX,BX,CX?

parsing:

NB's move instructions

MOV General register, data # MOV Ax,1234hmov General Register, Register # mov Bx,ax/mov bx,ds (the value of the segment register is assigned to the General Register) MOV segment register, register # mov Ds,ax (because you cannot assign a value to a segment register directly, so Register as intermediary) MOV memory unit, registers # MOV [0],ax (To assign values in the AX register to ds*16+0 this internal memory element) MOV memory Unit, register # MOV ax,[0] (the value assigned to the AX register in the unit ds*16+0)

sub,add Directive

Data segment

What we're doing here is actually a data segment, specifically how to manipulate the data segment

Operation of the accumulated 123b0h~123bah memory unit

Summary:

(1) When the word is stored in memory, to be stored with two contiguous memory units , the lower byte of the word is stored in the low address unit, the high byte is stored in the higher address unit.
(2) with the MOV instruction to access the memory unit, you can only give the unit offset address in the MOV instruction, at this time, the segment address by default in the DS register.
(3)[address] represents a memory unit that is offset to address.
(4) When transferring font data between memory and registers, the high address unit corresponds to a high 8-bit register, a low address cell, and a low 8-bit register.
(5) MOV, add, sub is an instruction with two Operation objects. JMP is an instruction that has an action object.

(2) In memory, case 3.6 shows

Initial value of each register: cs=2000h,ip=0,ds=1000h,ax=0,bx=0;

① writes out the sequence of instructions executed by the CPU (written out with assembly instructions).

② writes the values of CS, IP, and related registers after each instruction is executed by the CPU.

③ again: Is there a difference between the data and the program? How can I determine what data is in memory and what is a program?

Answer: I thought that the value of CP will change after jmp, in fact it is the inside of JMP Cp:ip

Instruction sequence		Cs	Ip	Ds	Ax	Bx
Initial value		2000h	0	0	0	0
1	MOV ax,6622h	2000h	3h	0	6622h	0
2	JMP 0ff0:0100	ff0h	100h	0	6622h	0
3	MOV ax,2000h	ff0h	103h	0	2000h	0
4	MOV Ds,ax	ff0h	105h	2000h	2000h	0
5	MOV Ax,[8]	ff0h	108h	2000h	c389h	0
6	MOV ax,[2]	ff0h	10bh	2000h	ea66h	0

Assembly language--register (Memory access DS data segment register, SS stack segment register)