Controlling Power Consumption in VHDL or Verilog

Use UCF file:

NET net_name PWR_MODE={LOW | STD};

If you need to preserve an internal logic node, use the KEEP attribute in the UCF file.

NET net_name KEEP;

When assigning attributes to bus (vector) elements, the name generated in the netlist will be the bus name and subscript seperated by an underscore. For example if the design contined a bus Q with subsripts 3 downto 0, then you would use Q_3 as the net name in the UCF to assign an attribute to subscript 3 of Q.