难道FPGA（XC2S15）是假的？？

我在写程序时，出现ERROR “The idcode read MCS form the device does not match the idcode in the bsdl file.\"
  为何？救救我？？

具体情况是这样的

ERROR:iMPACT:583 - \'1\': The idcode read from the device does not match the idcode in the bsdl File.
INFO:iMPACT:1578 - \'1\':  Device IDCODE :          00001111111111111111111111111110
INFO:iMPACT:1579 - \'1\': Expected IDCODE:    00000000011000001000000010010011
PROGRESS_END - End Operation.
Elapsed time =     11 sec.


为何？？