Registrer Addressing

Direct/Absolute Addressing

the operand is in a memory location; the address of this location is given explicitly in the instruction.

eg: Move LOC, R2

the operand is given explicitly in the instruction eg: Move #300,R0

Add #6,R1 Effective address = value

The Efficitive address of the oprand is the contents of a register or memory loc whose address appears in the instruction

We denote a indirection by placing the name of register or memory address given in the instruction in parentheses.

The register or memory location contains the address of operand is called a pointer

eg: Add (R1),R0

Index mode - the effective address of the operand is generated by adding a constant value to the contents of a register

index register holds address of a new location and calure of X defines an offset(displacement)

eg: Add 20(R1),R2

R1+20 is the correct address of the value we need

X(Ri) -> Ea = [Ri] + X

(Ri,Rj) -> Ea = [Ri] + [Rj]

X(Ri,Rj) -> Ea = [Ri] + [Rj] + X

EA is determined by index mode using the program counter in place of the general purpose register.

eg: X(PC) ; EA = [PC] + X (X is a signed number)

The effective address of the oprand is the contents of a register specified in the instruction

After accessing the opteand , the contents of this register are increment automatically eg: (Ri) -> Ea = Ri

Increment Ri

Contents of a register specified in the instruction is automatically decremented and used as effective address of the operand

(Ri) -> Decrement Ri

Ea = Ri

EffectiveAddressing

Fetch the contents of the memory location pointed to by the PC.The contents of this location are loaded into the IR.

Executes the instruction in the IR

singlebusOrganization

MDR has 2 input and 2 output

MAR- input[ processpr bus to MAR ] and 2 output

Control signals - controll all the operation , connected to the memory bus

General Purpose Registers [R0, … R(n-1)]

Y,Z,Temp -store value

img 2

Ri out is set ot 1 -> out is possble Rj in is set to 1 -> input is possible