Function 05h	Extended Communication Port Control		(PS/2)
entry   AH      05h 
	AL      00h     read modem control register 
		return  BL      modem control reg (see AL=1) 
	AL      01h     write modem control register 
	BL      modem control register: (for AL=00 and AL=01)  bits 
		0       data terminal ready 
		1       request to send 
		2       out1 
		3       out2 
		4       loop 
		5,6,7   reserved 
return  AH      status