Can problems occur when /WRITE is toggled during a Virtex serial configuration?
A problem only occurs if all three of the following conditions are met:
- /CS and /WRITE lines are both used as user I/Os after configuration
- /CS is Low during configuration
- /WRITE toggles during configuration
If all of these conditions are met, configuration fails and DONE does not go High. You can toggle PROG and reload the configuration without one of the above conditions to obtain a successful configuration.
If you can control the timing of the signal toggling, because the failure only occurs when /WRITE is toggled at the very end of the configuration. If the second and third conditions listed above are stopped 75% of the way into the configuration or earlier, the process should not fail.
NOTE: This information only applies to Virtex and Spartan-II devices. Virtex-E, Spartan-IIE, Virtex-II, and Spartan-3 devices do not have this problem.