Microprocessor and Computer Architecture

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Operation Code and Operands

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.

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.

  • 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.
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  • 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)

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