don't modify data bus when accessing unknown address

[fpga-games] / galaxian / src / roms.v

diff --git a/galaxian/src/roms.v b/galaxian/src/roms.v
index 2ca0d07c7e0c4c96fd81aa991158a6ad04b9dc6d..bdaf1306ab77f72c5d9bc7b669bb3f82bcb13087 100644 (file)
--- a/galaxian/src/roms.v
+++ b/galaxian/src/roms.v
@@ -1,9 +1,11 @@
 module galaxian_roms(
+I_CLK_18432M,
 I_CLK_12M,
 I_ADDR,
 O_DATA
 );
 
+input I_CLK_18432M;
 input I_CLK_12M;
 input [18:0]I_ADDR;
 output [7:0]O_DATA;
@@ -76,6 +78,7 @@ GALAXIAN_1H H_ROM(
 );
 
 reg [7:0]DATA_OUT;
+reg [7:0]DATA_OUT2;
 
 //    address map
 //--------------------------------------------------
@@ -122,10 +125,15 @@ begin
                DATA_OUT <= 8'h00;
        end
        else begin
-               DATA_OUT <= 8'h00;
+               DATA_OUT <= DATA_OUT;
        end
 end
 
-assign O_DATA = DATA_OUT;
+always@(negedge I_CLK_18432M)
+begin
+       DATA_OUT2 <= DATA_OUT;
+end
+
+assign O_DATA = DATA_OUT2;
 
 endmodule