Simulation environments

Hello,

In QUARTUS is included the simulator (I think Quartus use Modelsim in the background), but somepeople use directly Modelsim IDE.

What is the difference between the different kind of simulations?

Usually in quartus I generate a VECTOR WAVEFORM file, and then I add the nodes.

I am also trying to simulate a PLL that was generated with the MEGAWIZARD PLUG IN MANAGER, but in the simulation its output is always ZERO.

Do I have to add somekind of libraries to simulate a PLL.

thank you.

DABG