Operation Code and Operands

Opcodes:

Opcodes mean “operation codes”. 

• An opcode is the first part of an instruction that tells the computer what function to perform.

• Every computer has an operation code or opcode for each of its functions.

• It is an instruction that tells the processor what to do with the variable or data written beside it.

Operand:

An operand is the second part of the instruction, which tells the computer where to find or store the data or instructions. The number of operands varies among computers.

• Each instruction tells the Control Unit of the CPU what to do and how to do it.

• The operations are Arithmetic, Logical, Branch operation, etc. depending upon the problem that is given to the computers.

Note:

• The Intel 8085 is an 8-bit microprocessor that was widely used in early computing devices.
• It uses a set of instructions, each represented by a unique operation code (opcode), along with operands to perform various tasks.

Here are some common operation codes and their corresponding operands in the Intel 8085 assembly language:

• MOV (Move):
  • Opcode: MOV
  • Operands: MOV Rd, Rs
  • Example: MOV B, A (copies the contents of register A to register B)
• ADD (Addition):
  • Opcode: ADD
  • Operands: ADD R
  • Example: ADD B (adds the contents of register B to the accumulator)
• SUB (Subtraction):
  • Opcode: SUB
  • Operands: SUB R
  • Example: SUB C (subtracts the contents of register C from the accumulator)
• INR (Increment):
  • Opcode: INR
  • Operands: INR R
  • Example: INR D (increments the contents of register D by 1)
• DCR (Decrement):
  • Opcode: DCR
  • Operands: DCR R
  • Example: DCR E (decrements the contents of register E by 1)
• MVI (Move Immediate):
  • Opcode: MVI
  • Operands: MVI R, data
  • Example: MVI A, 20H (loads the immediate value 20H into register A)
• HLT (Halt):
  • Opcode: HLT
  • Operands: None
  • Example: HLT (halts the microprocessor)
• JMP (Jump):
  • Opcode: JMP
  • Operands: JMP address
  • Example: JMP 2000H (jumps to the memory address 2000H)
• CALL (Call Subroutine):
  • Opcode: CALL
  • Operands: CALL address
  • Example: CALL 3000H (calls a subroutine at the memory address 3000H)
• RET (Return from Subroutine):
  • Opcode: RET
  • Operands: None
  • Example: RET (returns from a subroutine)