Question

Explain direct and immediate addressing modes of Intel 8085 with suitable examples.

Answer 1

Direct addressing mode:

1) In direct addressing, the address appears after opcode of the instruction in program memory.

2) The address of the operand is specified within the instruction

3) The instructions using direct addressing mode are three-byte instructions. Byte 1 is opcode of the instruction, Byte 2 is lower order address and Byte 3 is high order address.

4) For e.g. LDA 9FFFH

i.e. This instruction loads accumulator with the content of memory location 9FFF H

Immediate addressing mode:

1)In Immediate addressing the data appears immediately after opcode of the instruction in program memory.

2)In these instructions, the actual data is specified within the instruction.

3) These operations are specified with either 2 or 3-byte instructions.

4) For e.g. ADI 05H

i.e. This instruction adds immediate data 05 H to the content of accumulator. The result is stored in an accumulator.