Verilog Circuits Sequential Logic ---- Sequential Logic Counters (2)

 3.2.2 Counters

3.2.2.1 Four-bit binary counter（Count15）

3.2.2.2 Decade counter（Count10）

3.2.2.3 Decade counter again（Count1to10）

3.2.2.4 Show decade counter（Countslow）

3.2.2.5 Counter 1-12（Exams/ece241 2014 q7a）

3.2.2.6 Counter 1000（Exams/ece241 2014 q7b）

3.2.2.7 4-digit decimal counter（Countbcd）

3.2.2.8 12-hour clock（Count clock）

3.2.2 Counters

3.2.2.1 Four-bit binary counter（Count15）

module top_module (
    input clk,
    input reset,      // Synchronous active-high reset
    output [3:0] q);
    
    always@(posedge clk)begin
        if(reset)begin
            q <= 4'd0;
        end
        else begin
            q <= q + 1'b1;
        end
    end
 
endmodule

这道题是要实现一个计数到15清零的计数器，大家注意，如果不是计数到15，需要加一个清零条件。这道题目可以不用添加。

3.2.2.2 Decade counter（Count10）

module top_module (
    input clk,
    input reset,        // Synchronous active-high reset
    output [3:0] q);
    
    always@(posedge clk)begin
        if(reset)begin
            q <= 4'd0;
        end
        else if(q == 4'd9)begin
            q <= 4'd0;
        end
        else begin
            q <= q + 1'b1;
        end
    end
 
endmodule

这道题目就需要加一个清零条件。

3.2.2.3 Decade counter again（Count1to10）

module top_module (
    input clk,
    input reset,
    output [3:0] q);
    
    always@(posedge clk)begin
        if(reset)begin
            q <= 4'd1;
        end
        else if(q == 4'd10)begin
            q <= 4'd1;
        end
        else begin
            q <= q + 1'b1;
        end
    end

这道题目修改了复位条件，改成了复位为1，原理是相同的。

3.2.2.4 Show decade counter（Countslow）

module top_module (
    input clk,
    input slowena,
    input reset,
    output [3:0] q);
    
    always@(posedge clk)begin
        if(reset)begin
            q <= 4'd0;
        end
        else if(slowena)begin
            if(q == 4'd9)begin
                q <= 4'd0;
            end
            else begin
                q <= q + 1'b1;
            end
        end
    end
 
endmodule

这道题多了一个使能信号，只有使能信号为高的时候计数器才开始工作，否则就保持原来的值。

3.2.2.5 Counter 1-12（Exams/ece241 2014 q7a）

module top_module (
    input clk,
    input reset,
    input enable,
    output [3:0] Q,
    output c_enable,
    output c_load,
    output [3:0] c_d
); //
    
    assign c_enable = enable;
    assign c_load = reset | ((Q == 4'd12) && enable == 1'b1);
    assign c_d = c_load ? 4'd1 : 4'd0;
 
    count4 u_counter (clk, c_enable, c_load, c_d, Q);
 
endmodule

3.2.2.6 Counter 1000（Exams/ece241 2014 q7b）

module top_module (
    input clk,
    input reset,
    output OneHertz,
    output [2:0] c_enable
); //
    wire[3:0]	one, ten, hundred;
    
    assign c_enable = {one == 4'd9 && ten == 4'd9, one == 4'd9, 1'b1};
    assign OneHertz = (one == 4'd9 && ten == 4'd9 && hundred == 4'd9);
 
    bcdcount counter0 (clk, reset, c_enable[0], one);
    bcdcount counter1 (clk, reset, c_enable[1], ten);
    bcdcount counter2 (clk, reset, c_enable[2], hundred);
 
endmodule

这两道题目都是例化作者已经写好的module从而创造一种新的计数器。

3.2.2.7 4-digit decimal counter（Countbcd）

module top_module (
    input clk,
    input reset,   // Synchronous active-high reset
    output [3:1] ena,
    output [15:0] q);
    
    reg [3:0]	ones;
    reg [3:0]	tens;
    reg [3:0]	hundreds;
    reg [3:0]	thousands;
    
    always@(posedge clk)begin
        if(reset)begin
            ones <= 4'd0;
        end
        else if(ones == 4'd9)begin
            ones <= 4'd0;
        end
        else begin
            ones <= ones + 1'b1;
        end
    end
    
    always@(posedge clk)begin
        if(reset)begin
            tens <= 4'd0;
        end
        else if(tens == 4'd9 && ones == 4'd9)begin
            tens <= 4'd0;
        end
        else if(ones == 4'd9) begin
            tens <= tens + 1'b1;
        end
    end
    
    always@(posedge clk)begin
        if(reset)begin
            hundreds <= 4'd0;
        end
        else if(hundreds == 4'd9 && tens == 4'd9 && ones == 4'd9)begin
            hundreds <= 4'd0;
        end
        else if(tens == 4'd9 && ones == 4'd9) begin
            hundreds <= hundreds + 1'b1;
        end
    end
    
    always@(posedge clk)begin
        if(reset)begin
            thousands <= 4'd0;
        end
        else if(thousands == 4'd9 && hundreds == 4'd9 && tens == 4'd9 && ones == 4'd9)begin
            thousands <= 4'd0;
        end
        else if(hundreds == 4'd9 && tens == 4'd9 && ones == 4'd9) begin
            thousands <= thousands + 1'b1;
        end
    end
    
    assign q = {thousands, hundreds, tens, ones};
    assign ena[1] = (ones == 4'd9) ? 1'b1 : 1'b0;
    assign ena[2] = (tens == 4'd9 && ones == 4'd9) ? 1'b1 : 1'b0;
    assign ena[3] = (hundreds == 4'd9 && tens == 4'd9 && ones == 4'd9) ? 1'b1 : 1'b0;
 
endmodule

这道题目大家只要掌握好清零条件和加一条件就好了。对于我的这种写法，更好的写法应该是讲条件单独用assign写下来，这样计数器的层次感比较强，代码可阅读性更好。下面的这道题目就是这种方式。

3.2.2.8 12-hour clock（Count clock）

module top_module(
    input clk,
    input reset,
    input ena,
    output pm,
    output [7:0] hh,
    output [7:0] mm,
    output [7:0] ss); 
    
    reg 		pm_temp;
    reg	[3:0]	ss_ones;
    reg [3:0]	ss_tens;
    reg	[3:0]	mm_ones;
    reg [3:0]	mm_tens;
    reg	[3:0]	hh_ones;
    reg [3:0]	hh_tens;
    wire		add_ss_ones;
    wire		end_ss_ones;
    wire		add_ss_tens;
    wire		end_ss_tens;
    wire		add_mm_ones;
    wire		end_mm_ones;
    wire		add_mm_tens;
    wire		end_mm_tens;
    wire		add_hh_ones;
    wire		end_hh_ones_0;
    wire		end_hh_ones_1;
    wire		add_hh_tens;
    wire		end_hh_tens_0;
    wire		end_hh_tens_1;
    wire		pm_ding;
    
    always@(posedge clk)begin
        if(reset)begin
            ss_ones <= 4'd0;
        end
        else if(add_ss_ones)begin
            if(end_ss_ones)begin
                ss_ones <= 4'd0;
            end
            else begin
                ss_ones <= ss_ones + 1'b1;
            end
        end
    end
    
    assign add_ss_ones = ena;
    assign end_ss_ones = add_ss_ones && ss_ones == 4'd9;
    
    always@(posedge clk)begin
        if(reset)begin
            ss_tens <= 4'd0;
        end
        else if(add_ss_tens)begin
            if(end_ss_tens)begin
                ss_tens <= 4'd0;
            end
            else begin
                ss_tens <= ss_tens + 1'b1;
            end
        end
    end
    
    assign add_ss_tens = end_ss_ones;
    assign end_ss_tens = add_ss_tens && ss_tens == 4'd5;
    
    always@(posedge clk)begin
        if(reset)begin
            mm_ones <= 4'd0;
        end
        else if(add_mm_ones)begin
            if(end_mm_ones)begin
                mm_ones <= 4'd0;
            end
            else begin
                mm_ones <= mm_ones + 1'b1;
            end
        end
    end
    
    assign add_mm_ones = end_ss_tens;
    assign end_mm_ones = add_mm_ones && mm_ones == 4'd9;
    
    always@(posedge clk)begin
        if(reset)begin
            mm_tens <= 4'd0;
        end
        else if(add_mm_tens)begin
            if(end_mm_tens)begin
                mm_tens <= 4'd0;
            end
            else begin
                mm_tens <= mm_tens + 1'b1;
            end
        end
    end
    
    assign add_mm_tens = end_mm_ones;
    assign end_mm_tens = add_mm_tens && mm_tens == 4'd5;
    
    always@(posedge clk)begin
        if(reset)begin
            hh_ones <= 4'd2;
        end
        else if(add_hh_ones)begin
            if(end_hh_ones_0)begin
                hh_ones <= 4'd0;
            end
            else if(end_hh_ones_1)begin
                hh_ones <= 4'd1;
            end
            else begin
                hh_ones <= hh_ones + 1'b1;
            end
        end
    end
    
    assign add_hh_ones = end_mm_tens;
    assign end_hh_ones_0 = add_hh_ones && hh_ones == 4'd9;
    assign end_hh_ones_1 = add_hh_ones && (hh_tens == 4'd1 && hh_ones == 4'd2);
    
    always@(posedge clk)begin
        if(reset)begin
            hh_tens <= 4'd1;
        end
        else if(add_hh_tens)begin
            if(end_hh_tens_0)begin
                hh_tens <= 4'd0;
            end
            else if(end_hh_tens_1)begin
                hh_tens <= hh_tens + 1'b1;
            end
        end
    end
    
    assign add_hh_tens = end_mm_tens;
    assign end_hh_tens_0 = add_hh_tens && end_hh_ones_1;
    assign end_hh_tens_1 = add_hh_tens && end_hh_ones_0;
    
    alwaysosedge clk)begin
        if(reset)beg@(p
in
            pm_temp <= 1'b0;
        end
        else if(pm_ding)begin
            pm_temp <= ~pm_temp;
        end
    end
    
    assign pm_ding = hh_tens == 4'd1 && hh_ones == 4'd1 && end_mm_tens;
    
    assign ss = {ss_tens, ss_ones};
    assign mm = {mm_tens, mm_ones};
    assign hh = {hh_tens, hh_ones};
    assign pm = pm_temp;
 
endmodule