8085 Microprocessor

6 Instruction Set

An instruction is a binary pattern designed inside a microprocessor to perform a specific function. Each instruction is represented by 8 bit binary value.

Types of instruction set:

1)      Data transfer instructions:

Instructions, which are used to transfer data from one register to another register, from memory to register or register to memory, come under this group. Examples are: MOV, MVI, LXI, LDA, STA etc. When an instruction of data transfer group is executed, data is transferred from the source to the destination without altering the contents of the source. For example, when MOV A, B is executed the content of the register B is copied into the register A, and the content of register B remains unaltered. Similarly, when LDA 2500 is executed the content of the memory location 2500 is loaded into the accumulator. But the content of the memory location 2500 remains unaltered.

 EXAMPLES:

1. MOV r1, r2 (Move Data; Move the content of the one register to another).  [r1] <-- [r2]

2. MOV r, m (Move the content of memory register). r <-- [M]

3. MOV M, r. (Move the content of register to memory). M <-- [r]

4. MVI r, data. (Move immediate data to register). [r] <-- data.

5. MVI M, data. (Move immediate data to memory). M <-- data.

6. LXI rp, data 16. (Load register pair immediate). [rp] <-- data 16 bits, [rh] <-- 8 LSBs of data.

7. LDA addr. (Load Accumulator direct). [A] <-- [addr].

8. STA addr. (Store accumulator direct). [addr] <-- [A].

9. LHLD addr. (Load H-L pair direct). [L] <-- [addr], [H] <-- [addr+1].

10.SHLD addr. (Store H-L pair direct) [addr] <-- [L], [addr+1] <-- [H].

11.LDAX rp. (LOAD accumulator indirect) [A] <-- [[rp]]

12.STAX rp. (Store accumulator indirect) [[rp]] <-- [A].

13.XCHG. (Exchange the contents of H-L with D-E pair) [H-L] <-->  [D-E].