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【应用手册】AN 578: Manual Placement of CMU PLLs and ATX PLLs in Stratix IV GX and GT Devices
This application note describes the steps involved in the manual placement of CMU
phase-locked loops (PLLs) and ATX PLLs in Altera’s Stratix® IV GX and GT FPGAs.
Altera’s Quartus® II software automatically places the CMU PLLs and ATX PLLs by
default.
The default placement of CMU PLLs by the Quartus II software may not be optimum
for all bonded configurations, except for the PCI Express (PIPE) ×8 bonded
configuration and the Basic ×8 bonded configuration. Check the default placement to
decide if it is optimum for skew requirements in your Basic (PMA Direct) ×N bonded
design. If it is not, manual placement of the CMU PLLs is recommended.
The default placement of ATX PLLs by the Quartus II software is performed
arbitrarily for all bonded configurations, except for the PCI Express (PIPE) ×8 bonded
configuration. Check the default placement to decide if it is optimum for skew
requirements in your design. If it is not, manual placement of the ATX PLLs is
recommended.
This application note uses the Basic (PMA Direct) xN bonded configuration as an
example scenario, where skew is a critical parameter and is dependent on the location
of the transmitter PLL (CMU PLL or ATX PLL).an578.pdf