一、题目
From a 1000 Hz clock, derive a 1 Hz signal, calledOneHertz, that could be used to drive an Enable signal for a set of hour/minute/second counters to create a digital wall clock. Since we want the clock to count once per second, theOneHertzsignal must be asserted for exactly one cycle each second. Build the frequency divider using modulo-10 (BCD) counters and as few other gates as possible. Also output the enable signals from each of the BCD counters you use (c_enable[0] for the fastest counter, c_enable[2] for the slowest).
The following BCD counter is provided for you.Enablemust be high for the counter to run.Resetis synchronous and set high to force the counter to zero. All counters in your circuit must directly use the same 1000 Hz signal.
module bcdcount ( input clk, input reset, input enable, output reg [3:0] Q );Module Declaration
module top_module ( input clk, input reset, output OneHertz, output [2:0] c_enable );
二、分析
子模块为10进制BCD码计数，每个计数器从0计数到9.将1000Hz分频为1Hz，可以使用三个计数器，分别计数个位，十位，百位，个位计满了十位开始计数，十位也计满了后百位开始计数。每个计数器的使能，表示该计数器开启计数。
三、代码实现
module top_module ( input clk, input reset, output OneHertz, output [2:0] c_enable ); // wire [3:0] q0,q1,q2; assign c_enable={q1==4'd9&&q0==4'd9,q0==4'd9,1'b1}; assign OneHertz = {q2 == 4'd9 && q1 == 4'd9 && q0 == 4'd9}; bcdcount counter0 (clk, reset, c_enable[0],q0); bcdcount counter1 (clk, reset, c_enable[1],q1); bcdcount counter2 (clk, reset, c_enable[2],q2); endmodule 或者 module top_module ( input clk, input reset, output OneHertz, output [2:0] c_enable ); // wire [3:0]cnt0,cnt1,cnt2;//分别是个位，十位，百位的计算器 bcdcount counter0 (clk, reset, c_enable[0],cnt0); bcdcount counter1 (clk, reset, c_enable[1],cnt1); bcdcount counter2 (clk, reset, c_enable[2],cnt2); assign c_enable[0]=1'b1;//个位的计算器一直在运行 assign c_enable[1]=(cnt0==4'd9)&c_enable[0];//个位计满并且还在计数时十位的计数器开始运行 assign c_enable[2]=(cnt0==4'd9&cnt1==4'd9)&c_enable[1];//个位数计满、十位计满并且还在计数时，百位的计数器开始运行 assign OneHertz=(cnt0==4'd9&cnt1==4'd9&cnt2==4'd9);//个十百位都计满9，即999，则为1Hz endmodule四、时序
