习题笔记 Exams/ece241 2014 q7b

使用BCD计数器从1000Hz生成1Hz信号

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该文描述了如何利用模10（BCD）计数器和一些门电路构建一个频率分频器，从1000Hz的时钟信号中衍生出每秒一次的1Hz信号，用于驱动小时/分钟/秒计数器创建数字挂钟。每个计数器的使能信号也被输出，以便于控制计数节奏。当计数达到999时，OneHertz信号被置为高电平，表示一秒钟的计时。

From a 1000 Hz clock, derive a 1 Hz signal, called OneHertz, 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, the OneHertz signal 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. Enable must be high for the counter to run. Reset is 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 top_module (
    input clk,
    input reset,
    output OneHertz,
    output [2:0] c_enable
); //
    reg [3:0]q0;
    reg [3:0]q1;
    reg [3:0]q2;
    
    bcdcount counter0 (clk, reset, c_enable[0],q0);
    bcdcount counter1 (clk, reset, c_enable[1],q1);
    bcdcount counter2 (clk, reset, c_enable[2],q2);
    
    assign c_enable[0] = 1'b1;  //q0为1000hz
    assign c_enable[1] = (q0[3] & ~q0[2] & ~q0[1] & q0[0]); // q0=9时进位；q1及c_enable[1]为100hz
    assign c_enable[2] = (q1[3] & ~q1[2] & ~q1[1] & q1[0] & q0[3] & ~q0[2] & ~q0[1] & q0[0]); //q1,q0=9时进位；q2及c_enable[2]为10hz
    
    assign OneHertz = ({q2,q1,q0}==12'b100110011001 ? 1'b1:1'b0);  //计数器到999时为高电平

endmodule