Function 01h	Send Character in AL to Comm Port DX (0 or 1)
entry   AH      01h 
	AL      character 
	DX      port number (0 or 1) 
return  AH      RS232 status code 
		bit     0       data ready 
			1       overrun error 
			2       parity error 
			3       framing error 
			4       break detected 
			5       transmission buffer register empty 
			6       transmission shift register empty 
			7       timeout 
	AL      modem status 
		bit	0	delta clear-to-send
			1       delta data-set-ready 
			2       trailing edge ring detected 
			3       change, receive line signal detected 
			4       clear-to-send 
			5       data-set-ready 
			6       ring received 
			7       receive line signal detected