Two down and dirty methods might be to set up the PLC com port as a modbus RTU slave or even a ASCI port.
The 1st would require a mobus master program on your Pc, the second use Hyperterminal on Pc and add to PLC program code to interegate serial string and convert it to a point/ value change.
The HMI option , Cimplicty ME view or a 50pt Cimplicity PE is far easier, and cheaper in the long run