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looks like you're trying to simulate Altera's actual HDL files. when in the MegaWizard click step 2 and create simulation models in your language of choice. then compile them into your ModelSim project instead of the HDL files you've been trying. this is probably worth a read:
http://www.altera.com/literature/hb/qts/qts_qii53014.pdf --- Quote End ---
Exactly. I am simulating the HDL files generated by Quartus IP MegaWizard. Thanks for putting the link there.
While I am studying it, could you please tell me if I can draw my own testbench waveform using Modelsim Altera (the same way with the what Quartus II does, e.g. insert node, node finder and so forth)? I tried to search on Internet but couldn't find any useful information...
Thank you!