don't modify data bus when accessing unknown address

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

//===============================================================================\r
// FPGA MOONCRESTA VIDO-MIX\r
//\r
// Version : 1.00\r
//\r
// Copyright(c) 2004 Katsumi Degawa , All rights reserved\r
//\r
// Important !\r
//\r
// This program is freeware for non-commercial use. \r
// An author does no guarantee about this program.\r
// You can use this under your own risk.\r
//\r
//================================================================================\r
\r
\r
module mc_vedio_mix(\r
\r
I_VID_R,\r
I_VID_G,\r
I_VID_B,\r
I_STR_R,\r
I_STR_G,\r
I_STR_B,\r
\r
I_C_BLnXX,\r
I_C_BLX,\r
I_MISSILEn,\r
I_SHELLn,\r
\r
O_R,\r
O_G,\r
O_B\r
\r
);\r
\r
input  [2:0]I_VID_R;\r
input  [2:0]I_VID_G;\r
input  [1:0]I_VID_B;\r
input  [2:0]I_STR_R;\r
input  [2:0]I_STR_G;\r
input  [1:0]I_STR_B;\r
\r
input  I_C_BLnXX;\r
input  I_C_BLX;\r
input  I_MISSILEn;\r
input  I_SHELLn;\r
\r
output [2:0]O_R;\r
output [2:0]O_G;\r
output [1:0]O_B;\r
\r
// MISSILE => Yellow ;\r
// SHELL   => White  ;\r
wire   W_MS_D = ~(I_MISSILEn & I_SHELLn);\r
wire   W_MS_R = ~I_C_BLX  & W_MS_D;\r
wire   W_MS_G = ~I_C_BLX  & W_MS_D;\r
wire   W_MS_B = ~I_C_BLX  & W_MS_D & ~I_SHELLn ;\r
\r
assign O_R = I_C_BLnXX ? I_VID_R | I_STR_R | {1'b0,W_MS_R,W_MS_R}: 3'b000 ;\r
assign O_G = I_C_BLnXX ? I_VID_G | I_STR_G | {1'b0,W_MS_G,W_MS_G}: 3'b000 ;\r
assign O_B = I_C_BLnXX ? I_VID_B | I_STR_B | {     W_MS_B,W_MS_B}: 2'b00  ;\r
\r
endmodule