Instruction type LDA a16 in 8085 Microprocessor


In 8085 Instruction set, LDA is a mnemonic that stands for LoaD Accumulator with the contents from memory. In this instructionAccumulatorwill get initialized with 8-bit content from the 16-bit memory address as indicated in the instruction as a16. This instruction uses absolute addressing for specifying the data. It occupies 3-Bytes in the memory. First Byte specifies the opcode, and the successive 2-Bytes provide the 16-bit address, i.e. 1-Byte each for each memory location.

Mnemonics, Operand Opcode(in HEX) Bytes
LDA Address 3A 3

Let us consider LDA 4050H as an example instruction of this type. It is a 3-Byte instruction. The initial content of memory address 4050H is ABH. Initially Accumulator content is CDH. As after execution A will be initialized with value ABH. Memory location 4050H will still remain with the content ABH. The results of execution of this instruction is as below −

Before After
(4050) ABH ABH

Address Hex Codes Mnemonic Comment
2008 3A LDA 4050H A <- Content of the memory location 4050H
2009 50 Low order Byte of the address
200A 40 High order Byte of the address

Here is the timing diagram of the instruction LDA 4050H


Summary − So this instruction LDA 4050H requires 3-Bytes, 4-Machine Cycles (Opcode Fetch, Memory Read, Memory Read, Memory Read) and 13 T-States for execution as shown in the timing diagram.

Published on 30-Nov-2018 16:34:10