Is it possible to put a cable extension on the Xilinx XChecker or Parallel cables?
The length that a cable can be extended depends solely on the port (Parallel, Serial, USB). In brief, extending the cable might cause data corruption due to attenuation of the signals and should be avoided.
For a serial port:
An extra 5 feet should be okay. The RS-232C standard allows cable lengths up to 15 meters. The RS-423 and RS-422 allow up to 700 meters and 1300 meters respectively; however, they are not as widespread in computers. Make sure to use a good extension cable that is firmly connected and away from possible noise sources.
You cannot use an extension. You cannot extend the cable because the parallel port drivers are not strong enough. The signals will attenuate, the data will become corrupted.
NOTE: Make sure that your parallel cable is not running through a dongle. There have been cases where removing the dongle resolved programming issues.