Which HMI haev you bought. If it is the panelview 550 or higher you are better off getting the unit with DH485 (NOT RS232 DH485) as it has both a DH485 In and DH485 out. You can link the panelview to the SLC5/03 DH485 port, then connect your pic to the panelview DH485 and communicate with both the PLC and HMI at once. The other way to do it is use an AIC unit and build a small DH485 network which willl allow you to connect the PLC, HMI & Laptop at once.