ERROR: [Drc 23-20] Rule violation (NSTD-1) Unspecified I/O Standard - 3 out of 3 logical ports use I/O standard (IOSTANDARD) value 'DEFAULT', instead of a user assigned specific value. This may cause I/O contention or incompatibility with the board power or connectivity affecting performance, signal integrity or in extreme cases cause damage to the device or the components to which it is connected. To correct this violation, specify all I/O standards. This design will fail to generate a bitstream unless all logical ports have a user specified I/O standard value defined. To allow bitstream creation with unspecified I/O standard values (not recommended), use set_property SEVERITY {Warning} [get_drc_checks NSTD-1]. Problem ports: clk, din, dout.