rom.vhd

design compile synthesis user guide

package ROMS is
  -- declare a 5x8 ROM called ROM
  constant ROM_WIDTH: INTEGER := 5;
  subtype ROM_WORD is BIT_VECTOR (1 to ROM_WIDTH);
  subtype ROM_RANGE is INTEGER range 0 to 7;
  type ROM_TABLE is array (0 to 7) of ROM_WORD;
  constant ROM: ROM_TABLE := ROM_TABLE'(
      ROM_WORD'("10101"),              -- ROM contents
      ROM_WORD'("10000"),
      ROM_WORD'("11111"),
      ROM_WORD'("11111"),
      ROM_WORD'("10000"),
      ROM_WORD'("10101"),
      ROM_WORD'("11111"),
      ROM_WORD'("11111"));
end ROMS;

use work.ROMS.all;   -- Entity that uses ROM
entity ROM_5x8 is
  port(ADDR: in ROM_RANGE;
       DATA: out ROM_WORD);
end;

architecture BEHAVIOR of ROM_5x8 is
begin
  DATA <= ROM(ADDR);      -- Read from the ROM
end BEHAVIOR;