solution

 

The into instruction generates an overflow interrupt (interrupt 4) if the overflow flag is set. Overflow interrupt is a trap, and therefore the interrupt instruction is not restarted. Write an interrupt handler to replace the system-supplied one. Your interrupt handler should display the message, “An overflow has occurred” and then replace the result with zero. As a part of the exercise, test that into does not generate an interrupt unless the overflow flag is set.

Convert toupper.asm given in Chapter 9 into an interrupt handler for interrupt 100. You can assume that DS:BX points to a null-terminated string. Write a simple program to test your interrupt handler.