First VHDL try

in VHDL 'X' means Unknown, not dont care, dont care is '-'

But VHDL also has strong typing, so comparing an input of 4 bits to "1XXX" will look for that string literally during simulation, so "1000 will NOT match, only "1XXX" will match.

To do what you are doing, you need to use the matching case statement from VHDL 2008 (case?), that will try and match dont cares:

case? a is
  when "0100000110-00100" => dq(8 downto 1) <= "10111111"; 
  when "01--------00----" => dq(8 downto 1) <= "01111111";
--etc

otherwise, if you're stuck with VHDL 93, you can use the std_match function from the std_logic_misc library

if std_match(a, "01000000110-00100") then
---
elsif std_match(a, "01--------00----") then
--etc

This way simulation will match your hardware.