The JTAG circuitry used on the Avnet MiniZed is a Xilinx solution based on the FTDI FT2232. As stated in https://www.xilinx.com/support/answers/68889.html, "the proprietary solution is not documented or supported, and cannot be provided to customers as a reference."
Please do NOT use the FT_PROG tool in conjunction with the MiniZed. The only way to fix it after erasing it is to send it back to the factory, which is more expensive than just buying a new MiniZed.
Bryan