这个可以参考下：
#Created by Constraints Editor (xc3s500e-pq208-5) - 2013/01/07
NET "clk" LOC = P82;
NET "clk" TNM_NET = "clk";
TIMESPEC TS_clk = PERIOD "clk" 20 ns HIGH 50 %;
NET "clk" IOSTANDARD = LVCMOS33;
NET "Seg[0]" IOSTANDARD = LVCMOS33;
NET "Seg[1]" IOSTANDARD = LVCMOS33;
NET "Seg[2]" IOSTANDARD = LVCMOS33;
NET "Seg[3]" IOSTANDARD = LVCMOS33;
NET "Seg[4]" IOSTANDARD = LVCMOS33;
NET "Seg[5]" IOSTANDARD = LVCMOS33;
NET "Seg[6]" IOSTANDARD = LVCMOS33;
NET "dp" IOSTANDARD = LVCMOS33;
NET "tar[0]" IOSTANDARD = LVCMOS33;
NET "Seg[0]" LOC = P102;
NET "Seg[1]" LOC = P99;
NET "Seg[2]" LOC = P107;
NET "Seg[3]" LOC = P109;
NET "Seg[4]" LOC = P112;
NET "Seg[5]" LOC = P100;
NET "Seg[6]" LOC = P106;
NET "dp" LOC = P108;
NET "tar[0]" LOC = P57;
# PlanAhead Generated IO constraints
NET "an[0]" IOSTANDARD = LVCMOS33;
NET "an[1]" IOSTANDARD = LVCMOS33;
NET "an[2]" IOSTANDARD = LVCMOS33;
NET "an[3]" IOSTANDARD = LVCMOS33;
NET "an[4]" IOSTANDARD = LVCMOS33;
NET "an[5]" IOSTANDARD = LVCMOS33;
NET "an[6]" IOSTANDARD = LVCMOS33;
NET "an[7]" IOSTANDARD = LVCMOS33;
NET "an[0]" LOC = P132;
NET "an[1]" LOC = P129;
NET "an[2]" LOC = P128;
NET "an[3]" LOC = P127;
NET "an[4]" LOC = P126;
NET "an[5]" LOC = P123;
NET "an[6]" LOC = P122;
NET "an[7]" LOC = P120;
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