Internal register type

Internal register type

contain 14 individual 16 Bit register , According to the function, it can be divided into 3 class ：

8 General registers ;4 Segment registers ;2 Control registers .

1 General registers

① Data register (AX,BX,CX,DX);

8088/8086 contain 4 individual 16 Bit data register , It can also be divided into 8 individual 8 Bit register , namely ：
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Idioms specific to data registers ：

AX： accumulator , all I/O All instructions passed AX Transfer information with the interface , The results of intermediate operations are mostly placed in AX in ;

BX： Base register , Used to store base addresses in indirect addressing ;

CX： Count register , Used to store count values in loop or string operation instructions ;

DX： Data register , In indirectly addressed I/O Store... In the instruction I/O Port address ; stay 32 Bit multiplication and division , Store high 16 digit .

② Address register (SP,BP);

SP： Stack pointer register , Its content is the offset address of the top of the stack ;

BP： Base pointer register , It is often used to store the offset address of memory unit when accessing memory .

remarks ：BX And BP The difference in application , As a general register , Both can be used to store data ; Used as a base register BX Indicates that the data sought is in the data segment ; use BP Indicates that the data is in the stack segment .

③ Index register (SI,DI).

SI： Original index register

DI： Target index register

Index register is often used in instructions to store the address of data in memory .

2 Control register
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① Status flags

CF(carry flag)： Carry flag bit , Add and subtract , There is progress at the highest level / Borrowing rule CF=1

PF(parity flag)： Parity flag bit , The low of the result of the calculation 8 In a “1” When the number of is even ,PF=1

AF(auxiliary carry flag)： Auxiliary carry flag bit , Addition and subtraction operation , if bit3 towards bit4 With borrow and borrow spaces , be AF=1

ZF(zero flag)： Zero flag bit , When the operation result is zero ,ZF=1

SF(sign flag)： Symbol sign bit , When the highest bit of the operation result is 1 when ,SF=1

OF(overflow flag)： overflow flag , When the result of an arithmetic operation exceeds the expressible range of a signed number ,OF=1.

Status flags Example ：
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② Control flag bit

TF(trap flag)： Trap flag bit , Also called tracking flag bit ,TF=1 when , send CPU In the working mode of single step instruction

IF(interrupt flag)： Interrupt allow flag bit ,IF=1 send CPU Can respond to maskable interrupt requests .

DF(direction flag)： Direction sign bit , Determine the direction of operation during data string operation .

3 Segment register

CS： Code segment register , The base address of the code segment .

DS： Segment register , The segment base address where the data segment is stored .

ES： Additional segment register , The segment base address where the additional segment is stored .

SS： Stack segment register , The segment base address where the stack segment is stored .

The value of the segment register indicates the location of the response logical segment in memory .

Followed by – Memory addressing
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