General Description: What is the difference between .des (simulation) and .tve (waveform) files?
Saving and loading signals and stimulators (.tve)
If you save or load waveforms using binary (.tve) format, all stimuli are saved/loaded with waveforms. Currently-defined formulas are stored automatically in the file "project_name.frm" and are loaded at the simulator startup. If the automatic backup option (select Option -> Preferences from menu and choose the General tab) is set, the active waveforms can be stored automatically with the selected time period.
NOTE: Do not use the "Save Simulation State" option to save signals/stimulators. The saved simulation state will not work if you make changes to your circuit.
The "Save Waveform" window allows you to save the displayed signal waveforms in a binary test vector file or in a text (ASCII) test vector file.
Extracts from the Foundation Simulator On-line Help:
Save/Load Simulation State files (.des)
Simulation files represent work in progress. They contain the design status that existed in the Foundation simulator after the last simulation step. This simulation status is stored in a set of design tables that contain information about device connections, waveform diagrams, states of sequential logical devices, JEDEC fuse maps, hex files, position of switches and jumpers, simulation settings, etc.
Simulation files represent a concrete schematic design implementation. If that schematic undergoes any changes, a new design file must be generated for the schematic.
Simulation data is created on-the-fly during the loading of a schematic netlist. This design data is continuously updated with new test vectors, hex data, JEDEC fuse maps, etc., as they are being loaded into the simulator and with a new signal and internal states during simulation. You may save this design information at any time using the "Save Simulation State" option.
You can load and save design files by selecting the "Load Simulation State" and "Save Simulation State" options, which are located in the File menu. (These options will display the "Load Simulation" and "Save Simulation" windows, respectively.
NOTE: Do not use simulation state files (.des) instead of test vector files. A loaded simulation file works correctly only if you have not made any changes in your design since saving the file.