Interrupt  0Ch  Communications Controller (serial port) hdw. entry
(0:0030h)  (IRQ4)  Serial Port 1 (com1) or modem in PCjr or Convertible 
note    IRQ 4 may be used by SDLC (synchronous data-link control) or  
	bisynchronous communications cards instead of a serial port. 
(internal) stack fault (80286 protected-mode) 
	Generated on stack overflow/underflow. Note that the 80286 will shut 
	down in real mode if SP=1 before a push.