fix clock for LRAM
[fpga-games] / galaxian / src / mc_clock.v
... / ...
CommitLineData
1//---------------------------------------------------------------------\r
2// FPGA MOONCRESTA CLOCK GEN \r
3//\r
4// Version : 1.00\r
5//\r
6// Copyright(c) 2004 Katsumi Degawa , All rights reserved\r
7//\r
8// Important !\r
9//\r
10// This program is freeware for non-commercial use. \r
11// An author does no guarantee about this program.\r
12// You can use this under your own risk.\r
13//\r
14//---------------------------------------------------------------------\r
15\r
16\r
17\r
18module mc_clock(\r
19\r
20I_CLK_36M,\r
21O_CLK_18M,\r
22O_CLK_12M,\r
23O_CLK_06M,\r
24O_CLK_06Mn\r
25\r
26);\r
27\r
28input I_CLK_36M;\r
29output O_CLK_18M;\r
30output O_CLK_12M;\r
31output O_CLK_06M;\r
32output O_CLK_06Mn;\r
33\r
34// 2/3 clock divider(duty 33%)\r
35//I_CLK 1010101010101010101\r
36//c_ff10 0011110011110011110\r
37//c_ff11 0011000011000011000\r
38//c_ff20 0000110000110000110\r
39//c_ff21 0110000110000110000\r
40//O_12M 0000110110110110110\r
41reg [1:0] state;\r
42reg clk_12m;\r
43initial state = 0;\r
44initial clk_12m = 0;\r
45\r
46// 2/3 clock (duty 66%)\r
47always @(posedge I_CLK_36M)\r
48begin\r
49 case (state)\r
50 2'd0: state <= 2'd1;\r
51 2'd1: state <= 2'd2;\r
52 2'd2: state <= 2'd0;\r
53 2'd3: state <= 2'd0;\r
54 endcase\r
55\r
56 if (state == 2'd2)\r
57 clk_12m = 0;\r
58 else\r
59 clk_12m = 1;\r
60end\r
61\r
62assign O_CLK_12M = clk_12m;\r
63\r
64reg CLK_18M;\r
65always @(posedge I_CLK_36M)\r
66begin\r
67 CLK_18M <= ~ CLK_18M;\r
68end\r
69assign O_CLK_18M = CLK_18M;\r
70\r
71// 1/3 clock divider (duty 50%)\r
72reg CLK_6M;\r
73reg CLK_6Mn;\r
74\r
75always @(posedge O_CLK_12M)\r
76begin\r
77 CLK_6M <= ~CLK_6M;\r
78 CLK_6Mn <= CLK_6M;\r
79end\r
80\r
81assign O_CLK_06M = CLK_6M;\r
82assign O_CLK_06Mn = CLK_6Mn;\r
83\r
84endmodule\r
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