Chapter 2 knowledge Summary

2.1 General registers

1, ax, BX, CX, dx is called General Register

2. Ax can be divided into ah, Al ......

 

Storage of 2.2 characters in registers

1. byte: it is recorded as byte. A byte consists of 8 bits.

Word: it is recorded as word. A word consists of two bytes: high (AH) and low (al)

 

Several hundred thousand Assembly commands

1,

MoV ax 18 AX = 18

MoV Ah 78 Ah = 78

Add ax 8 AX = AX + 18

MoV ax bx ax = Bx two objects have the same number of digits

Add ax bx ax = AX + bx two objects have the same number of digits

 

2.4 physical address

The address of the memory unit is called a physical address.

This physical address must be formed internally before the CPU sends a physical address to the address bus.

 

2.5 16-bit CPU

16-bit 8086cpu

The worker can process up to 16 data records at a time.

The maximum width is 16 characters.

The path between the register and the register is 16 bits.

 

2.6 8086cpu physical address

1. When the 8086cpu needs to read/write the memory:

The CPU-related components provide two 16-bit addresses, one called the segment address and the other called the offset address.

The segment address and offset address are sent to a part called the address divider through the internal bus.

The address divider combines two 16-bit addresses into a 20-bit physical address.

The address divider sends 20-bit physical addresses to the input/output control circuit through the internal bus.

The Input/Output Control Circuit sends 20-bit physical addresses to the address bus.

20-bit physical address is transferred to the memory by the address bus

2. physical address = segment address * 16 + offset address

 

2.9-segment register

8086 a total of four segment registers: CS, DS, SS, es

 

2.10 CS and IP

In the 8086 host, the CPU executes the Cs: IP point content as a command at any time.

 

2.11 modify CS and IP commands

MoV command cannot be used to set CS and IP value

Commands that can change the cs ip value are called transfer commands.

JMP segment address: the offset address can be used to modify the content of CS and IP addresses at the same time.

A valid JMP Register uses the value in this register to modify the IP address.

 

Chapter 2 knowledge Summary