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AR# 35689

ModelSim SE 6.5c causing incorrect phase fuctionality with PLL


There is a known issue when simulating ModelSim SE 6.5c and the UNISIM PLL model.

If you configure CLKOUT0 and CLKOUT1 of the PLL equally but add a 180 degree phase shift to CLKOUT1, the phase shift is not reflected in the simulation.

u_pll_adv : PLL_ADV
CLKOUT0_DIVIDE => value,
CLKOUT0_PHASE => 0.000,
CLKOUT1_PHASE => 180.000,


This is a known issue specific to ModelSim 6.5c.

Workaround 1:
Add the "-novopt" option to the vsim command with ModelSim SE 6.5c.

Workaround 2:
Use a different version of ModelSim, for example ModelSim SE 6.6a.
AR# 35689
Date Created 05/14/2010
Last Updated 09/24/2014
Status Active
Type Known Issues
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