Re: VHDL RTL question
Each tristated output is controlled by one signal, which may be the same signal that controls other outputs. If the input to your decoder never changes, the tristate outputs are either always on or always off. Either the decoder never gets the value that enables the tristate buffers, or the decoder is implemented incorrectly.
If the decoder inputs are supposed to come from the chip pins, it's also possible that you didn't do what is necessary to connect the inputs to any of the chip pins. I'm not familiar with Quartus, so I can't give you a checklist for this task.