The Waveform window lets you review the state of multiple signals as the simulation runs. However, due to its limited size, the number of signals you can effectively monitor in the Waveform window is limited. To identify design failures during debugging, you might need to trace more signals and objects than can be practically displayed in the Waveform window. You can log the waveforms for signals that are not displayed in the Waveform window, by writing them to the simulation waveform database (WDB). After simulation, you can review the transitions on all signals captured in the waveform database file.
In the Scope window, right-click on dut
under testbench. Click Log to Wave Database from the
options list. Select Objects in Scope option. The
specified signals are written to a waveform database.