Assembly language: Chapter II Register

A typical CPU consists of an operator, a controller, a register, and an internal bus that connects parts of the device

Registers are parts that programmers can read and write with instructions, and control the CPU by altering the contents of the registers.

The number structure of different CPU registers is not the same, 8086 has 14 registers

2.1 General-Purpose registers

8086 all registers are 16 bits, can hold 2 bytes, AX, BX, CX, DX for storing general data, become General register

To be compatible with the old 8-bit registers, each 16-bit register can be divided into 2 separate 8-bit registers to use, with the names of Ah, Al to represent high 8-bit and low 8-bit

Storage of 2.2 words in registers

Bytes byte: Can be stored in a 8-bit register

Word Word: is two bytes, which can be stored in a 16-bit register, the high 8-bit byte of the modifier and the low 8-bit byte are stored in high 8-bit registers and low 8-bit registers

A font data 20000 is stored in Microsoft Dynamics AX, the height of 8 bits is 78, the low 8 bits is 32, can be regarded as a font data 20000, can also be seen as two separate registers stored 78 and 32 respectively

hexadecimal data Each two bits represents a 8-bit, the hexadecimal representation of the data to see the high and low register is very convenient as in Ax is 4e20h, then AH is 4eh,al is 20H.

2.3 Several assembly instructions

MOV ax,18: send 18 into Register AX Advanced language: ax=18

Add ax,8: Add 8 Advanced language to data in register AX: ax=ax+8

Note: If the result of the operation exceeds the range of values that the register can represent, it will be truncated

The number of operand bits of the assembly instruction must be the same

Detection 2.1:

1> writes out the values in the relevant registers after each assembly instruction is completed:

mov ax,62627 ax=f4a3h

mov ah,31h ax=31a3h

mov al,23h ax=3123H

Add Ax,ax ax=6246H

mov bx,826ch bx=826CH

mov cx,ax cx=6246H

mov ax,bx ax=826CH

Add ax,bx ax=04d8h

mov al,bh ax=0482H

mov ah,bl ax=6c82h

Add Ah,ah ax=d882h

Add al,6 ax=d888h

Add Al,al ax=d810h

mov ax,cx ax=6246H

The 2> uses only mov,add instructions and does not exceed 4 instructions to calculate 2 of the 4-time Square

MOV ax,0002h

Add Ax,ax

Add Ax,ax

Add Ax,ax

　　

Assembly language: Chapter II Register