A320
Flight Crew Last 90 Days 250; Flight Crew Total 17000; Flight Crew Type 3000
Confusion; Human-Machine Interface
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Declared Emergency
Aircraft
After takeoff at approximately 8;000 MSL we had an ECAM; EGT Limit Exceeded No. 1 Engine. Captain flew the aircraft while I ran the ECAM. A red tick mark was present on the No. 1 EGT gauge. Upon reducing thrust between MCT and CLIMB detent the EGT was back in limits and thrust lever remained in CLM detent until completion of ECAM and emergency declared and emergency return to the field coordinated. Captain left thrust levers in CL detent with auto thrust engaged until hand flying the visual approach. Limits were never again exceeded.During the return to field the FMGC would not take the foreign airport identifier as a new destination. Four attempts were made by First Officer and verified by Captain. We even tried the alternate three letter identifier but that did not work either. We elected to not get fixated on automation and loaded the XR ILS manually and flew a visual approach to the runway. Could not get landing performance data and contacting Dispatch at the critical time was considered too distracting during the landing phase. The overweight landing checklist was accomplished with the noted exception of land performance data. Landing was uneventful. Write ups for over temp and overweight landing were accomplished by Maintenance.
An A320 flight crew declared an emergency and returned to their departure airport for an overweight landing following a left engine over temperature event.  During the return some FMS and performance data functions failed to function.