General Description: FPGA Express ignores LOC attributes in CPLDs if the IOB is configured as a 3-state I/O. If the I/O is configured as an input or an output, the LOC attribute will be written to the netlist; however, a LOC attribute for a 3-state I/O will be ignored and is not written into the netlist.
解决方案
To work around this issue, write the LOC constraints into the UCF file.