Register indirect addressing mode in 8085 Microprocessor

Register indirect mode in 8085 microprocessors is an addressing mode in which the address part of the instruction specifies the address of the register, and the register holds the effective address of the operand. The operand is present in the effective address specified by the register. In this article, we will explore register indirect addressing mode in 8085 microprocessors in detail along with examples. Also, we will discuss the advantages and disadvantages and applications of register indirect addressing modes.

Register Indirect Mode in 8085 Microprocessor

The register indirect mode in the 8085 microprocessor is the addressing mode in which the register specifies the effective address of the operand. In other words, in the register indirect mode in the 8085 microprocessor, the operand is present in the address specified in the register in the instruction. In this addressing mode, the address of the operand is specified indirectly by using the register.

8085 Microprocessor Instruction with Register Indirect Mode

Representation of 8085 microprocessor instruction with register indirect addressing modes.

Opcode Destination Operand, Source Operand
Opcode Register, Register

Operations on Register Indirect Addressing Mode

In register indirect addressing mode, we require following operations to fetch the operand.

• First identify the register from the specified address in the instruction.
• Then, go to the register and get the content of the register which gives us the effective address of the operand.
• Then, go to the specified effective address.
• The content present in the effective address gives us the operand on which operations is to be performed.

Examples of 8085 Microprocessor Instruction with Register Indirect Mode

Some examples of register indirect addressing modes in 8085 microprocessors are given below.

Instructions of 8085 microprocessor (register indirect addressing mode used)	Description
MOV A, M	This instruction stores the data present in the address specified in the H-L registers to the accumulator.
LDAX B	This instruction stores the content of the address specified in the BC register to the accumulator.
STAX B	This instruction stores the content of the accumulator to the memory address specified by the BC register.

Advantages and Disadvantages of Register Indirect Mode in 8085 Microprocessor

Some advantages and disadvantages of register indirect mode are listed below.

Advantages of Register Indirect Mode in 8085 Microprocessor

Some advantages of register indirect mode are listed below.

• The register indirect addressing mode provides the reusability of the code i.e., same code can be used any number of times.
• The address part of the instruction in register indirect addressing mode points the address of the register, which is small hence, making the size of the instruction smaller.

Disadvantages of Register Indirect Mode in 8085 Microprocessor

Some disadvantages of register indirect mode are listed below.

• The register indirect addressing mode involves the memory access two times which increases the memory references.
• In register indirect addressing mode, the time required to fetch the operand is more due to increase in the memory access.

Applications of Register Indirect Addressing Mode

The main application of the register indirect addressing mode is that it is used implement pointers. Some applications of register indirect mode are listed below.

• Register indirect addressing mode is used to implement pointer.
• Register indirect addressing mode can be used to pass an array.

Conclusion

From the above discussion we can conclude that the 8085 microprocessors have different addressing modes. In the register indirect mode of 8085 microprocessor the address of the operand is specified by the register given in the instruction. The operand is fetched from the address specified in the register present in the instruction and then the desired operation is performed on it.

FAQs-Register indirect addressing mode in 8085 Microprocessor

What is Effective Address?

The address where the operand is stored is called the effective address.

What is Addressing Mode?

The addressing modes defines and specifies the data on which the operations are to be performed. These addressing modes tell us about the operand in which the desired operation is performed.

What are the Addressing Modes in 8085 Microprocessor?

The different addressing modes in 8085 microprocessors are:

• Immediate Addressing Mode
• Register Addressing Mode
• Direct Addressing Mode
• Register Indirect Addressing Mode
• Implied Addressing Mode
• Relative Addressing Mode