INSTRUCTION FORMAT IN COA

Instruction Format

An instruction format defines:

ü  Operands reside in the memory are specified by their memory address.

ü  Operands residing in the processor register are specified by the register address.

ü  A register address is a binary number of k bits that define one of the 2^k  registers of the CPU.

a)     3 ADDRESS

b)    2 ADDRESS

c)     1 ADDRESS

d)    0 ADDRESS

These can be explain by taking an example:

X= (A+B)*(C+D)

Ø   3 ADDRESS:

ADD       R1,A,B            R1<-M[A]+M[B]

ADD        R2,C,D          R2<-M[C]+[D]

MUL       X,R1,R2          M[X]<-R1*R2

Ø  2 ADDRESS:

MOV        R1,A            R1<-M[A]

ADD         R1,B           R1<-R1+M[B]

MOV        R2,C           R2<-M[C]

ADD         R2,D           R2<-R1+M[D]

MUL         R1,R2         R2<-R2*R1

MOV         X,R2           M[X]<-R2

Ø  1 ADDRESS:

LOAD        A                 AC<-M[A]

ADD          B                  AC<-AC+M[B]

STORE      T                 M[T]<-AC

LOAD        C               AC<-M[C]

ADD          D                  AC<-AC+M[D]

MUL         T                  AC*M[T]

STORE     X                 M[X]<- AC

Ø  0 ADDRESS

PUSH       A              TOS<-A

PUSH       B              TOS<-B

ADD                         TOS<-(A+B)

PUSH       C             TOS<-C

PUSH       D              TOS<-D

ADD                         TOS<-(C+D)

MUL                         TOS<-(A+B)*(C+D)

POP         X                M[X]<-TOS

In my next post I will explain about addressing mode.

Author : Unknown

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