Types of Addressing modes

 

  1. Implied / Implicit Addressing Mode
  2. Stack Addressing Mode
  3. Immediate Addressing Mode
  4. Direct Addressing Mode
  5. Indirect Addressing Mode
  6. Register Direct Addressing Mode
  7. Register Indirect Addressing Mode
  8. Relative Addressing Mode
  9. Indexed Addressing Mode
  10. Base Register Addressing Mode
  11. Auto-Increment Addressing Mode
  12. Auto-Decrement Addressing Mode

1. Implied Addressing Mode-

 

In this addressing mode,

  • The definition of the instruction itself specify the operands implicitly.
  • It is also called as implicit addressing mode.

 

Examples-

 

  • The instruction “Complement Accumulator” is an implied mode instruction.
  • In a stack organized computer, Zero Address Instructions are implied mode instructions.

(since operands are always implied to be present on the top of the stack)

 

2. Stack Addressing Mode-

 

In this addressing mode,

  • The operand is contained at the top of the stack.

 

Example-

 

ADD

  • This instruction simply pops out two symbols contained at the top of the stack.
  • The addition of those two operands is performed.
  • The result so obtained after addition is pushed again at the top of the stack.

 

3. Immediate Addressing Mode-

 

In this addressing mode,

  • The operand is specified in the instruction explicitly.
  • Instead of address field, an operand field is present that contains the operand.

 

 

Examples-

 

  • ADD 10 will increment the value stored in the accumulator by 10.
  • MOV R #20 initializes register R to a constant value 20.

 

4. Direct Addressing Mode-

 

In this addressing mode,

  • The address field of the instruction contains the effective address of the operand.
  • Only one reference to memory is required to fetch the operand.
  • It is also called as absolute addressing mode.

 

 

Example-

 

  • ADD X will increment the value stored in the accumulator by the value stored at memory location X.

AC ← AC + [X]

5. Indirect Addressing Mode-

 

In this addressing mode,

  • The address field of the instruction specifies the address of memory location that contains the effective address of the operand.
  • Two references to memory are required to fetch the operand.

 

 

Example-

 

  • ADD X will increment the value stored in the accumulator by the value stored at memory location specified by X.

AC ← AC + [[X]]

 

6. Register Direct Addressing Mode-

 

In this addressing mode,

  • The operand is contained in a register set.
  • The address field of the instruction refers to a CPU register that contains the operand.
  • No reference to memory is required to fetch the operand.

 

 

Example-

 

  • ADD R will increment the value stored in the accumulator by the content of register R.

AC ← AC + [R]

 

NOTE-

 

It is interesting to note-

  • This addressing mode is similar to direct addressing mode.
  • The only difference is address field of the instruction refers to a CPU register instead of main memory.

 

7. Register Indirect Addressing Mode-

 

In this addressing mode,

  • The address field of the instruction refers to a CPU register that contains the effective address of the operand.
  • Only one reference to memory is required to fetch the operand.

 

 

Example-

 

  • ADD R will increment the value stored in the accumulator by the content of memory location specified in register R.

AC ← AC + [[R]]

 

NOTE-

 

It is interesting to note-

  • This addressing mode is similar to indirect addressing mode.
  • The only difference is address field of the instruction refers to a CPU register.

 

8. Relative Addressing Mode-

 

In this addressing mode,

  • Effective address of the operand is obtained by adding the content of program counter with the address part of the instruction.

 

Effective Address

= Content of Program Counter + Address part of the instruction

 

 

NOTE-

 

  • Program counter (PC) always contains the address of the next instruction to be executed.
  • After fetching the address of the instruction, the value of program counter immediately increases.
  • The value increases irrespective of whether the fetched instruction has completely executed or not.

 

9. Indexed Addressing Mode-

 

In this addressing mode,

  • Effective address of the operand is obtained by adding the content of index register with the address part of the instruction.

 

Effective Address

= Content of Index Register + Address part of the instruction

 

 

10. Base Register Addressing Mode-

 

In this addressing mode,

  • Effective address of the operand is obtained by adding the content of base register with the address part of the instruction.

 

Effective Address

= Content of Base Register + Address part of the instruction

 

 

11. Auto-Increment Addressing Mode-

 

  • This addressing mode is a special case of Register Indirect Addressing Mode where-

 

Effective Address of the Operand

= Content of Register

 

In this addressing mode,

  • After accessing the operand, the content of the register is automatically incremented by step size ‘d’.
  • Step size ‘d’ depends on the size of operand accessed.
  • Only one reference to memory is required to fetch the operand.

 

Example-

 

 

Assume operand size = 2 bytes.

Here,

  • After fetching the operand 6B, the instruction register RAUTO will be automatically incremented by 2.
  • Then, updated value of RAUTO will be 3300 + 2 = 3302.
  • At memory address 3302, the next operand will be found

12. Auto-Decrement Addressing Mode-

 

  • This addressing mode is again a special case of Register Indirect Addressing Mode where-

 

Effective Address of the Operand

= Content of Register – Step Size

 

In this addressing mode,

  • First, the content of the register is decremented by step size ‘d’.
  • Step size ‘d’ depends on the size of operand accessed.
  • After decrementing, the operand is read.
  • Only one reference to memory is required to fetch the operand.

 

Example-

 

Comments

Post a Comment

Popular posts from this blog

DBMS - Program 6 - Insurance Database

Image
  6. INSURANCE DATABASE Consider the Insurance database given below. The primary keys are underlined and the data types are specified. PERSON (Driverld: text; Name: text; Address: text) CAR (RegNo: text; Model: text; Year: number) OWNS (DriverId: text; RegNo: text) ACCIDENT (ReportNo: number, AccDate: Date; Location: text) PARTICIPATED (DriverId; text; RegNo: text; ReportNo; number, Dmg_Amt:number (10, 2)) a)   Create the above tables by specifying the primary and foreign keys. b) Enter at least five tuples for each relation c)   Update the damage amount for each car accident. d) Add a new accident to the database. e)   Find the total number of people who owned cars that were involved in accidents in the                                                                                              year 2002. f)   Find the number of accidents in which cars belonging to a specific model were involved. g) Display the owners and their car deta ils.   Cre
Read more

Java - Swing

  Swing  is a Java Foundation Classes JFC] library and an extension of the Abstract Window Toolkit [AWT]. Swing offers much-improved functionality over AWT, new components, expanded components features, excellent event handling with drag and drop support. Introduction of Java Swing Swing has about four times the number of User Interface [U1] components as AWT and is part of the standard Java distribution. By today’s application GUI requirements, AWT is a limited implementation, not quite capable of providing the components required for developing complex GUI’s required in modern commercial applications. The AWT component set has quite a few bugs and really does take up a lot of system resources when compared to equivalent Swing resources. Netscape introduced its Internet Foundation Classes [IFC] library for use with Java. Its Classes became very popular with programmers creating GUI’s for commercial applications. Swing is a Set Of API ( API- Set Of Classes and Interfaces ) Swing is Pro
Read more