Program

• 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.