Spartan3 XC3S50AN，片内自带FLASH，目前情况为：可以program FPGA Only,无法Program Flash and FPGA
M0M1M2 设置为110，M0M1分别通过10K电阻上拉，M2通过82欧电阻下拉
一共做了六块板子，其中有四块可以烧，有两块换过很多FPGA芯片，仍然无法烧写，重做板子也无法烧写，是否和芯片有关？四块可以烧写的芯片为第一次购入。
JTAG连接应该没有问题，因为可以program FPGA Only
Console提示内容为:
done.
PROGRESS_END - End Operation.
Elapsed time =      0 sec.
'1': Loading file 'E:/C.bit' ...
done.
Found sync word in bitstream.
UserID read from the bitstream file = 0xFFFFFFFF.
INFO:iMPACT:501 - '1': Added Device xc3s50an successfully.
----------------------------------------------------------------------
----------------------------------------------------------------------
INFO:iMPACT - Current time: 2016/6/30 1:01:22
PROGRESS_START - Starting Operation.
Maximum TCK operating frequency for this device chain: 10000000.
Validating chain...
Boundary-scan chain validated successfully.
'1': SPI access core not detected. SPI access core will be downloaded to the device to enable operations.
INFO:iMPACT - Downloading core file D:/ISE/14.4/ISE_DS/ISE/spartan3a/data/xc3s50an_spi.cor.
'1': Downloading core...
LCK_cycle = NoWait.
LCK cycle: NoWait
done.
'1': Reading status register contents...
INFO:iMPACT:2219 - Status register values:
INFO:iMPACT - 0011 1111 1110 1100
INFO:iMPACT:2492 - '1': Completed downloading core to device.
INFO:iMPACT - SPI Device not found.
INFO:iMPACT:2488 - The operation did not complete successfully.
'1': Configuration data download to FPGA was not successful. DONE did not go high, please check your configuration setup and spi mode settings.
PROGRESS_END - End Operation.
Elapsed time =     61 sec.

主要问题应该是这一句：INFO:iMPACT - SPI Device not found.

请问是怎么回事？有没有什么解决的方案？
芯片换过很多批了，一直无法解决