INT 4A - TI Professional PCIBM PC - KEYBOARD - GET KEYBOARD STATUS
	AH = 01h
Return: ZF set if no keystroke available
	ZF clear if keystrokes in buffer
	    AX = next keystroke (AH=00h for ASCII keys -- no scan code)
SeeAlso: AH=00h,AH=02h,AH=03h,AH=04h,AH=05h,INT 16/AH=01h