"Final review" 16/32-bit microprocessor (8086) basic register

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1.8086 Programming structure （ Leave a suspense ）

8086 have 16 Bit microprocessor ,16 Data line and 20 Root address line . Because available 20 Bit address , So the addressable address space can reach 2^20 Byte is （1MB）

Functionally ,8086 In two parts , namely Bus interface unit （BIU bus interface unit） and Executive parts （EU execution unit ）

I'm learning 8086 First understand the programming structure of 16/32 Bit microprocessor basic register

2.16/32 Bit microprocessor basic register

On the whole, it can be divided into 3 class ：

• General registers （8 individual ）

• Segment register （4 individual ）

• Instruction pointer and flag register （2 individual ）

2.1 General registers

General register function ： It can store operands and addresses for logical operations and arithmetic operations .

Pointer and index register functions ： Those who participate in the address operation are mainly in the pointer and index register group 4 A register SP/BP/SI/DI, Generally used to store the offset of the address .

32 The bit register is 16 The bit register name is prefixed with E, Such as EAX, Expanded 16~31 position

 Why are general registers classified as high 8 Bit and low 8 position ？

 For example, data storage starts from the low order , Our calculation only uses low 8 When a , high 8 Bits can also participate in the calculation , Not idle waste , Such fine division improves memory utilization ; Such a 16 Bit registers can be used as 2 individual 8 Bit register use 

（ shorthand ：ABCDX BSP SDI ）

1. AX It's called an accumulator （Accumulator）

   Most frequently used , For arithmetic 、 Logic operation and transmitting information with peripherals

2. BX It's called the base register （Base address Register）

   Commonly used as the offset address of the storage address , Used to store base addresses in indirect addressing

3. CX It's called a counter （Counter）

   As Loop and string operations Wait for the counter in the instruction , Number of storage cycles or repetitions

4. DX It's called a data register （Data register）

   The height commonly used to store double word length data 16 position , Or in indirectly addressed I/O Store... In the instruction I/O Port address .

5. SP/ESP Stack pointer register

   Used to indicate the address of the current top of the stack in the stack segment . Push (PUSH) And out of the stack (POP) Instructions from SP Give the offset address of the top of the stack . Therefore, it is necessary to register with stack segment SS In combination with , To point to the storage unit at the top of the stack .

6. BP/EBP Base pointer register

   Indicate the base address of the data to be processed in the stack segment , Therefore, it is called base pointer register . You can also store the offset of the address at the top of the stack , At this time, the default segment is stack segment SS.

   SP and BP Register and SS Segment registers are used together to determine the address of the storage unit in the stack segment

   BX And BP Similarities and differences in application

   As a general register , Both can be used to store data ;

   As a base register ,BX Usually used to address data segments DS;

   BP Is usually used to address stack segments SS. BX The base register is generally the same as DS or

7. SI Is the source address register （Source Index）

   Point to the unit where the source data is located

8. DI Is the destination address register （Destination Index）

   But with SI/ESI（ Source index register ） In combination with , Point to the unit where the destination data is located ;

except Stack pointer register SP/ESP Cannot be used as an index register , The other seven general registers can be used for address calculation Used to store the operands involved in the operation

2.2 Segment register

Alias ： Segment selector , Others call it Segment selector .

The register storing the high-order address is called segment register , low 16 Bit addresses are called offsets , Put it in the general register , Such as base register BX

4 A basic segment register , Used to divide memory space into different segments

among ES,FS,GS, Are called additional segment registers ,FS,GS yes 32 A new addition to bit microprocessors

Why is there a general register , Also design segment registers ？

The segment register is designed for convenience CPU Secondary addressing , Because the memory space is very large , If there are only general registers , When there's a lot of data ,CPU Efficiency will decrease when accessing data , Segment space with segment register ,CPU When addressing, you can first find the segment register , Then look for the data stored in the general register

1. Code segment CS(code segment)

   It is used to store the currently running program . The segment address of the segment where the current execution program is stored , Move its contents to the left 4 Bit plus IP The content of the pointer is the address of the next execution instruction .

2. Data segment DS(data segment)

   Used to store the data used in the program （ Such as numerical value 、 character 、 Address ）. The segment address where the current data segment is stored , Move its contents to the left 4 To add the calculated offset address is to read the specified unit of the data segment / Write the address .

3. stack segment SS(stack segment)

   It is a special storage area opened up in memory , Used to temporarily save the data in the register . The segment address where the current stack segment is stored , Move its contents to the left 4 Bit plus SP The content of is Top address

4. Additional segment ES(extra segment)

   Is additional data , Used to store the destination operand in a string operation instruction

Stack stack , What's the difference between a heap and a stack ？？？ The heap determines the memory size at run time , The stack determines the memory size at compile time

The difference between heap and stack - Fat hair - Blog Garden (cnblogs.com)

Rules for using segment registers ：

2.3 Flag and instruction pointer registers

1. EIP/IP Instruction pointer register

   be used for The offset of the address of the unit where the instruction is stored , And code segment register CS In combination with , In order to get the address of the unit where the instruction is located .IP The address is constantly changing , Until the end of the program .(cs and ip I'm a good brother )

2. EFR/FR（EFLAGS/FLAGS） Flag register

   16 Only one of them is used 9 position , For storing the system Status flag and Control signs .

   Status flag ： yes CPU Generated during the execution of instructions .

   1） sign indicator SF（sign flag） Value is equal to the highest bit of the operation result

   2） Zero mark ZF (zero flag) The result of operation is 0, The value is 1; Otherwise, it's worth 0

   3） Parity mark PF (parity flag) The operation result is low 8 There are even numbers of bits 1 Then the value is 1

   4） Carry mark CF (carry flag) Addition makes the highest bit carry or subtraction makes the highest bit borrow , Then the value is 1

   5） Auxiliary carry flag AF (auxiliary flag) 8 Bit binary addition operation makes 3 In the first place 4 Bits have carry or subtract operations to make the th 3 In the first place 4 There is a borrowed space , Then the value is 1; Also known as the semi carry flag

   6） Overflow sign OF (overflow flag) Overflow during operation , Then the value is 1： Use Double sign bitwise exclusive or evaluation

   Control signs ： It is used to control the operation of the microprocessor and the working mode of the system

   1） Direction signs DF (direction flag) ： If IF Set up “1”, be CPU Maskable interrupt requests can be accepted ; conversely , be CPU Maskable interrupt requests cannot be accepted .

   2） Interrupt allow flag IF (interrupt enable flag)

   3） Tracking signs TF (trap flag) Also known as trap sign

Example ： There may be exam questions here , So we should remember each symbol bit and its meaning

3. Q & A

Rules for using segment registers ？

8086CPU Yes 20 Root address line , The maximum addressable memory space is 1MB. and 8086 The only registers of are 16 position . use 16 Address addressing of bits 1MB Space is impossible . So we need to segment the memory , That is the 1MB Space is divided into 2⁴ , namely 16 Segments , Each paragraph does not exceed 64KB（2^16,16 Bit data lines can be addressed ）.

But the segment register is still 16 Bit , Its content represents the height of the segment base 16 position , This 16 Add... After the address of bit 4 individual 0 It constitutes 20 Segment base address of bit . And the original 16 The offset in the address segment is only the bit . such , A complete physical memory address consists of two parts , high 16 Segment base address and low bit 16 In segment offset of bit , Of course they have 12 Bits overlap , Their two parts are added together , To form a complete physical address .

4. View of

1. Please name three kinds of buses in the computer and their respective functions ？

• data bus ： The data bus is CPU And memory 、CPU And I/O Interface device To transmit between Various Instruction data information Bus of , These signals go back and forth through the data bus , therefore , The information on the data bus is Two way transmission Of .

• Address bus ： What is transmitted on the address bus is CPU To memory 、I/O Interface device Address information sent , Addressing capability is CPU Unique function , Address information is only provided by CPU issue , therefore , The information on the address bus is One way transmission Of .

• Control bus ： The control bus transmits various control signals , Yes CPU To memory 、I/O Of interface equipment Control signals , Yes I/O The interface is sent to CPU Of Answer signal 、 Request signal , therefore , The information on the control bus is Two way transmission Of .

2. Say the rules of using registers in the microprocessor ？

CS and IP Use it with ：CS It is used to store the currently running program . The segment address of the segment where the current execution program is stored ,IP be used for The offset of the address of the unit where the instruction is stored ,** take CS Its content moves left 4 Bit plus IP The content of the pointer is the address of the next execution instruction .**IP The address is constantly changing , Until the end of the program .(cs and ip I'm a good brother )

SS and SP Use it with ：SS It is a special storage area opened up in memory , Used to temporarily save the data in the register . The segment address where the current stack segment is stored ,SP Give the offset address of the top of the stack , take SS Move content left 4 Bit plus SP The content of is Top address

3. The known logical address is 1F02H：38A0H How to calculate its corresponding physical address ？

   1 F 0 2 0 H
 +   3 8 A 0 H
---------------
   2 2 8 C 0 H

4. Please draw Pentium Register and name of processor （ General registers 、 Segment register 、 Instruction pointer and flag register ）