Depending on what method of communication you require from the PLC and the LCD unit itself?
You can have TCP/IP (Industrial Ethernet), RS232, Profibus, Foundation fieldbus, Modbus, Hardwired I/O etc from a PLC.
If you are referring to LCD Process panels (typically an interface in the field that allows a user to monitor the plant process without having to visit the Scada in the control room) they interface in many industrial communication standards. (I think to any of the ones mentioned above) Applications are endless.