Program

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  • A set of instructions that perform a task is called a program usually a program is stored in the memory.
  • The processor then fetches the instructions comprising the program from memory one at a time and perform the desired operations.
  • The computer is under control of stored program,except for the possibility of external interruption from the operator or by I/O devices connected to the machine.
  • The operation of the CPU is determined by the instructions it executes.
  • These instructions are referred to as machine instructions or computer instructions.
  • The collection of different instructions that the CPU can execute is referred to as the CPU‟s instruction set.
  • Example Program
                          Compute (X+Y)Z
                          MVI B, X
                          MVI A,Y
                          ADD B 
                          STA 5000H
                          HLT

Assembly Language Programming

Types of Instructions
  • An assembly language program is written using suitable combinations of the instructions drawn from the instruction set.
  • An instruction may be 1, 2 or 3 bytes in length.
  • In any of these three types of instructions
    • The first byte indicates the operation to be performed.
    • The second and third bytes if present contain either the operand or address of the operand on which the operation is to be performed.

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