Question

1. Initialize CS=OD03 and IP = 0000 2. Assemble the following set of instructions at CS:IP Step-la: PUSH DS Step-1b: MOV AX, 0000 Step-1c: PUSH AX Step-1d: MOV CX, 0005 Step-le: MOV DX, 0000 Step-1f: NOP Step-Ig: INC DX Step-1h: LOOP 000B Step-li: RETIF 3. Execute the instructions one at a time with TRACE commands. Describe the operation performed by each instruction. Note down your observations to any changes in as much detail as possible. a) Instruction-a b) Instruction-b c) Instruction-c d) Instruction-d e) Instruction-e 1) Instruction-f g) Instruction-g h) Instruction-h i) Instruction-i

Answer 1

cs and ip intialise the address from where the program should be started

Instruction A: pushes the value present in the ds register to stack segment

Instruction B: AX register is stored with value 00

Instruction C: the value stored in ax register is pushed to stack segment

Instruction D: cx register is loaded with value 0005

Instruction E: dx register is loaded with 0000

Instruction F: NOP means no operation,used to create some time delay

Instruction G: DX=DX+1 implies dx=0+1=1

Instruction H: jumps to the address 000B , loop function jumps to the given address and reduces cx value by 1(dec cx) ,implies it produces 5 iterations as cx=5

Instruction I: RET function returns the executing unit to the next instruction present after CALL / INTERRUPT function,whose address value was previously pushed into stack segment (pop function  is used to retrieve the adresss)