Indirect Addressing Mode in Assembly Language

29 Apr 2023 Balmiki Mandal 0 Assembly language

Indirect Addressing Mode in Assembly Language Programming

Assembly language programming is characterized by the use of several addressing modes to reference data. Indirect addressing mode is one of the most common and powerful address modes used by assembly language programmers. In this mode, a register or memory location is used to hold the address of the data to be used. This allows for greater flexibility when accessing data within a program, as the address can be changed without having to rewrite the code.

How Does Indirect Addressing Work?

In assembly language programming, the indirect addressing mode is represented by two parentheses “( )” surrounding a register or memory location. For example, if the instruction is to move data from one location to another, it would be written as “MOV X, (Y)”. In this case, Y would be the register or memory location that holds the address of the data to be moved.

The indirect addressing mode allows for the data being operated on to point to a different location than the instruction. This is especially useful for operations such as loading data from an array, or looping through a list of items. By simply changing the address held in the register or memory location, the data being used can be changed without having to modify any code.

 

Note

  • The instruction Specifies a Register that contains the address of the operand
  • Both Internal and External RAM can be indirectly addressed
  • Address register can be R0 or R1 of a selected register bank the SP for 8 bit and DPTR for 16 bit address

 

Possibilities for Internal RAM

  • MOV  @Ri,A              ;i=0/1
  • MOV  A,@Ri             ;1=0/1
  • MOV  @Ri,ADDR
  • MOV ADDR,@Ri
MOV 0xD0,#0      ;use register bank 0
MOV R0,#0x3C    ;put 3Ch value in R0 register
MOV A,#34h       ;put 34h value accumulator
MOV @R0,#3      ;memory at 3C gets #3(it's decimal value) i,3;M[3C]<-3
MOV @R0,A        ;memory at 3C gets contains of 'A' register M[3C]<-34h

 

Advantages and Disadvantages

The main advantage of using the indirect addressing mode is its flexibility and ease of use. As previously mentioned, it is a powerful address mode that provides great control over accessing data within a program. Additionally, indirect addressing tends to require fewer lines of code than direct addressing.

On the other hand, there are some disadvantages to using indirect addressing. It can require more processing time than direct addressing, as the processor must determine the address at which the data is stored. There is also the risk of introducing bugs into your program due to incorrect addresses, as the wrong address could lead to accessing unexpected data.

Conclusion

Indirect addressing offers many advantages to assembly language programmers, including flexibility, ease of use, and efficiency. It is an essential part of assembly language programming and can be used for operations such as loading data from an array or looping through a list of items. While there are some disadvantages to its use, overall, it is an effective addressing mode that can be utilized to greatly improve the performance of your program.

BY: Balmiki Mandal

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