Interrupt  01h Single step
(0:0004h) Taken after every instruction when CPU Trap Flag indicates
	  single-step mode (bit 8 of FLAGS is 1). This is what makes the T
	  command of DEBUG work for single stepping. Is not generated after MOV
	  to segment register or POP of segment register. (unless you have a
	  very early INTEL\8088 with the microcode bug).