2) Explain what this program do?
Program 2:
MOV AL, 0H
MOV CX, 000AH
Again: ADD AL, 2H
DEC CX
JNZ Again
int 3
This program initializes the value of AL (accumulator register) to 0 and CX (counter register) to 10. It then enters a loop where it adds 2 to AL in each iteration and decrements CX until CX becomes zero. Once the loop is completed, the program generates a breakpoint interrupt (int 3) indicating the end of program execution. Therefore, this program adds the value 2 to the accumulator register AL, ten times, and then stops.
This program is written in x86 assembly language. Here is a step-by-step explanation of what it does:
1. MOV AL, 0H: This instruction moves the value 0H (which represents 0 in hexadecimal) into the AL register. AL is an 8-bit register that stores one byte of data.
2. MOV CX, 000AH: This instruction moves the value 000AH (which represents 10 in hexadecimal) into the CX register. CX is a 16-bit register that is commonly used as a counter or loop control variable.
3. Again: This is a label that marks the beginning of a loop.
4. ADD AL, 2H: This instruction adds the value 2H (which represents 2 in hexadecimal) to the current value in the AL register.
5. DEC CX: This instruction decrements the value in the CX register by 1.
6. JNZ Again: This instruction jumps to the label "Again" if the zero flag is not set. The zero flag is set when the result of the previous instruction is zero. In other words, this instruction makes the program loop back to the "Again" label if the value in the CX register is not zero.
7. int 3: This instruction generates a software interrupt 3. In x86 assembly language, the int 3 instruction is a "breakpoint" that is used for debugging purposes.
Therefore, this program initializes the AL and CX registers with specific values, enters a loop, adds 2 to the AL register in each iteration, decrements the CX register by 1, and repeats this process until the CX register becomes zero. Finally, it generates a breakpoint interrupt.