General purpose registers of 8085 microprocessor

This post covers a set of FAQs on general-purpose registers of 8085 microprocessor.

Describe the general-purpose registers of 8085 microprocessor

We know that the registers are all storage areas inside the microprocessor and are used for different purposes.

General-purpose Registers are used to store only the data that is being used by the program under execution and the results obtained from it. These general-purpose registers are user-accessible through programs.

Registers B, C, D, E, H, and L are the general-purpose registers in the 8085. They can also be called scratchpad registers. In almost all arithmetic and logical operations, these registers are used as the second operands, the first operand being the accumulator (A).

The general-purpose registers are all 8-bit registers in 8085 but they can be handled as 16-bit registers as well. This can be achieved by combining the register pairs B and C, D and E, and H and L to perform 16-bit operations.

They are then named register pairs BC, DE, and HL, respectively.

Among these pairs, HL has special significance. A few memory-related instructions of the 8085 use the HL pair as a memory pointer.

For example, in the instruction MOV A, M transfer the content of the memory location to which the HL pair is pointing, to the accumulator. The HL pair is pre-loaded with the memory address in which data is available.

Mention the utility of the general purpose registers

General-purpose registers store temporary data during program execution, which can also be stored in different accessible memory locations. But storing temporary data in memory requires bus access – hence more time is needed to store. Thus it is always advisable to store data in general-purpose registers.

The more the number of general-purpose registers, the more is flexibility in programming. So a microprocessor having more such registers is always advantageous.

In what other way HL pair can be used?

HL register pair can be used as a data pointer or memory pointer. A few memory-related instructions of the 8085 use the HL pair as a memory pointer.

For example, in the instruction MOV A, M transfer the content of the memory location to which the HL pair is pointing, to the accumulator. The HL pair is pre-loaded with the memory address in which data is available.

Related Posts

Here are links to the articles we published on the Architecture of the 8085 microprocessor.

Functional block diagram of Intel 8085 microprocessor and the functional units

General-purpose registers of 8085 microprocessor

Special-purpose registers of 8085 microprocessor – FAQs

Different Signals used in 8085 microprocessor & their significance – FAQs

Author of this post

This post is co-authored by Professor Saraswati Saha, who is an assistant professor at RCCIIT, a renowned degree engineering college in India. Professor Saha teaches subjects related to digital electronics & microprocessors.

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