Function 03h	Fetch the Status of Comm Port DX (0 or 1)
entry   AH      03h 
return  AH      set bits (01h) indicate comm-line status  
		bit     7       timeout 
		bit     6       empty transmit shift register 
		bit     5       empty transmit holding register 
		bit     4       break detected ("long-space") 
		bit     3       framing error 
		bit     2       parity error 
		bit     1       overrun error 
		bit     0       data ready 
	AL      set bits indicate modem status 
		bit     7       received line signal detect 
		bit     6       ring indicator 
		bit     5       data set ready 
		bit     4       clear to send  
		bit     3       delta receive line signal detect 
		bit     2       trailing edge ring detector  
		bit     1       delta data set ready 
		bit     0       delta clear to send