8088

IAPX 8088 is a member of intel architecture family introduced on june 1 1979, it is a 16-bit microprocessor means its register size is 16-bit.It is one of the most successful and selling microprocessor of intel and predecessor are intentel 88085 and intel 8086 which are of 8-bit microprocessor.

Intel calls its iapx 8088 menas intel advanced processor extension 8088 to this member of intel architecture.itwas very flexible and verstaile and it was first embedded in iBM PC.

This intel architecture is taken as example as computer architecture example as in continuation to previous post “computer architexture“.









IAPX 8088 register architecture

In this intel aechitecture, intel gives the name of its register as english alphabet like a,b,c,d.

General purpose registers

IAPX8088 has four general purpose registers and they are

AX is the accumulator register where all arithmetical and logical operations are done here.Here X means extended means it is of 16 bit.AX is used as one single 16- bit register or uses two 8 bit register as left 8-bit as AH (accunulator high) or as right 8-bit as AL(accumulator low), when any change is made in AH or AL ultimately changed in AX.

BX is rhe base reh=gister used to access memory location and it also general arithmetic operation is also done on it.

CX is the counter register used to store the count of the automatic instruction counter in iapx 8088.

DX is used to store thedestination of the I/O.

Index registers

Index registers are used to access memory like storing the address of source and destination location of memory during ab operation.They are 16-bit registers but they can’t use as 8-bit,8-bit register like general purpose registers.

SI and DI

SI means source index means it stores the source memory during an operation like string operation.

DI means destination index means it store the destination memory location during an operation like string operation.

Both SI and DI cans also perform arithmetic opereation like add and subtract.

IP

IP emans instruction pointer is used by the processor to track the movement of opcode of the instruction during the operation.It is under the control of the processor and it cannot perform any arithmetic operation.

BP

BP means base pointer is a special pointer/index regsiter used to access special section of the memory.

Flag register

Flag register in iapx 8088 is a 16-bit register,its each bit has special meaning and purpose.

Set means that value of single specific bit of flag register is 1.

Clear means the value of single specific bit of flag register is 0.

Now consider following diagram.

Carry (C)

Carry or C bit is used to store additional carry generated during mathematical operation like addition of 16-bit numbers.

The next bit after carry is undefined.

Parity (P)

Parity or P but is shows the numbers of 1’s in a word is odd or even.

The next bit after parity is undefined.

Auxillary carry (A)

Aucillary carry or A bit is set when in addition of hexadecimal numbers, carry is generated is moved from one nibble to another nibble.Ninnle is the set of 4 bits wich represent a hexadecimal number in binary number system.

The next bit after auxillary carry us undefined.

Zero (Z)

Zero or Z bit is set when the last mathematical or logical instruction peoduces a zero.

Sign (S)

Sign or S bit is set if the last mathematical operation done produces a negative sign.

Trap (T)

Trap or T bit is ls complex,it will be explain later.

Interrupt (I)

Interrupt or I is set when in some operation interruption from other i/o is isstopped for some interval during an opertation.

Direction (D)

Direction or S bit is used to know the direction when accessing memory.When it is 0 means accessing memory from down to up oe when it is 1 means accessing memory from up to down in a operation like string manipulation.

Overflow (O)

When in signed arithmetic the sign is change unexpecately due to an operation ,the overflow bit set.

All the bits after overflow are undefined.