新作了一块板子，JTAG直接 下载 程序失败， 但 IMPACT 可以识别FPGA,用示波器观察TDO，不下程序时为高电平，下载时一直为低电平，导致 INFO:iMPACT - 0000 0000 0000 0000 ，不知是什么原因，请大家帮个忙，谢谢。PS:板子采用主串模式，原理图有点问题，现在先只考虑JTAG直接下载程序。 原理图见附件。

IMPACT信息如下：

PROGRESS_END - End Operation.
Elapsed time = 0 sec.
Type = 0x0004.
ESN device is not available for this cable.
Attempting to identify devices in the boundary-scan chain configuration...
INFO:iMPACT - Current time: 2014/10/15 10:43:48
PROGRESS_START - Starting Operation.
Identifying chain contents...'0': : Manufacturer's ID = Xilinx xc6slx16, Version : 4
INFO:iMPACT:1777 - 
Reading D:/Xilinx/14.4/ISE_DS/ISE/spartan6/data/xc6slx16.bsd...
INFO:iMPACT:501 - '1': Added Device xc6slx16 successfully.
----------------------------------------------------------------------
----------------------------------------------------------------------
done.
PROGRESS_END - End Operation.
Elapsed time = 1 sec.
'1': Loading file 'E:/FPGAchengxu/FPGA_DSP1.0/top.bit' ...
done.
INFO:iMPACT:2257 - Startup Clock has been changed to 'JtagClk' in the bitstream stored in memory,
but the original bitstream file remains unchanged.
UserID read from the bitstream file = 0xFFFFFFFF.
Data width read from the bitstream file = 1.
INFO:iMPACT:501 - '1': Added Device xc6slx16 successfully.
----------------------------------------------------------------------
----------------------------------------------------------------------
INFO:iMPACT - Current time: 2014/10/15 10:44:10
PROGRESS_START - Starting Operation.
Maximum TCK operating frequency for this device chain: 25000000.
Validating chain...
Boundary-scan chain validated successfully.
'1': Programming device...
LCK_cycle = NoWait.
LCK cycle: NoWait
done.
'1': Reading status register contents...
[0] CRC ERROR : 0
[1] IDCODE ERROR : 0
[2] DCM LOCK STATUS : 0
[3] GTS_CFG_B STATUS : 0
[4] GWE STATUS : 0
[5] GHIGH STATUS : 0
[6] DECRYPTION ERROR : 0
[7] DECRYPTOR ENABLE : 0
[8] HSWAPEN PIN : 0
[9] MODE PIN M[0] : 0
[10] MODE PIN M[1] : 0
[11] RESERVED : 0
[12] INIT_B PIN : 0
[13] DONE PIN : 0
[14] SUSPEND STATUS : 0
[15] FALLBACK STATUS : 0
INFO:iMPACT:2219 - Status register values:
INFO:iMPACT - 0000 0000 0000 0000 
INFO:iMPACT:579 - '1': Completed downloading bit file to device.
INFO:iMPACT:188 - '1': Programming completed successfully.
LCK_cycle = NoWait.
LCK cycle: NoWait
INFO:iMPACT - '1': Checking done pin....done.
'1': Programming terminated. DONE did not go high.
PROGRESS_END - End Operation.
Elapsed time = 1 sec.

FPGA EXP Card_F.pdf