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AR# 14663

Virtex-II - DONE goes High even though the PROG pin is toggled during JTAG configuration


When the PROG pin is toggled during the configuration of a Virtex-II device, the DONE pin still goes High at the end of configuration; however, the device is not correctly programmed.


Under normal circumstances, the following events occur during Virtex-II JTAG configuration: 

- The synchronization word is sent to the device. 

- The Startup clock is set to "JTAG clock". 

- The CRC register is reset, then maintains a running CRC value. 

- Configuration information is sent to the device. 

- The running CRC value in the device is compared against the CRC value in the bit stream. 

- If no CRC error is detected, the JSTART command is sent to the JTAG Instruction Register. 

- The startup sequence is clocked by TCK. 


For complete details on this process, please refer to the "JTAG / Boundary Scan Programming Mode" section in the Configuration Chapter of the Virtex-II or Virtex-II Pro User Guide: 


Virtex-II Platform FPGA User Guide 


Virtex-II Pro and Virtex-II Pro X FPGA User Guide 


Asserting PROG on a Virtex-II device during configuration causes the following: 

- The startup clock setting is reset to its default value (JTAGCLK). 

- A loss of synchronization between the configuration logic and the bit stream occurs. 


A loss of synchronization means that the device does not recognize any further configuration data. No portion of the device is configured, no CRC check is performed, and a CRC error is not detected. 


When the JTAG JSTART command is sent to the (still unconfigured) device, the device enters the startup sequence, and DONE goes High.  


Related Documents 

- Virtex and Virtex-II FPGA synchronization: (Xilinx Answer 7891)  

- Virtex and Virtex-II FPGA CRC algorithm/check: (Xilinx Answer 6484) and (Xilinx Answer 14607) 

- Virtex FPGA startup sequence: (Xilinx Answer 8240) (This also pertains to Virtex-II.) 

- Effect of the PROG pin on the Virtex-II FPGA TAP: (Xilinx Answer 11508)

AR# 14663
Date Created 08/29/2007
Last Updated 05/14/2014
Status Archive
Type General Article