Compatibility between TTL output and LVTTL input
Basys3 IOs are either LVCMOS/LVTTL (2.5 to 3.3 V). Refer datasheet.http://www.xilinx.com/support/documentation/data_sheets/ds181_Artix_7_Data_Sheet.pdf

 It would be unsafe to use 5V TTL to drive them. Use voltage translators/buffers.

A simple way of translation between 3.3V -- 5V