可逆计数器设计实验

实验要求

实验步骤

74LS191模块代码

`timescale 1ns / 1ps
module cnt_74LS191(LD_, CT_, U_D, CP, D, Q, Max_Min, RCO_);
    input LD_, CT_, U_D, CP;
    input [3:0]D;

    output [3:0]Q;
    output Max_Min, RCO_;

    reg [3:0]Q;
    reg Max_Min;
    reg RCO_;

    always @(posedge CP or negedge LD_) begin
        if(!LD_) Q <= D;
        else if(CT_) Q <= Q;
        else begin
            if(!U_D) begin
                if(Q == 4'b1110) Max_Min <= 1;
                else Max_Min <= 0;
                Q <= Q + 4'b0001;
            end

            else begin
                if(Q == 4'b0001) Max_Min <= 1;
                else Max_Min <= 0;
                Q <= Q - 4'b0001;
            end   
        end
    end
    
    always @(CP) begin
        if(Max_Min == 1 && CP == 0) RCO_ <= 0;
        else RCO_ <= 1;
    end

endmodule

该程序的难点在于，要在合适的时候输出一个CP周期的Max_Min信号，和在合适的时候（Max_Min信号的后半个周期）输出半个CP周期的RCO_信号。（还是要实践出真知）

板极验证

使用的板卡型号：xc7a100tlcsg324-2L

set_property CLOCK_DEDICATED_ROUTE FALSE [get_nets LD_]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN V5} [get_ports LD_]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN T4} [get_ports CT_]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN V6} [get_ports U_D]
set_property CLOCK_DEDICATED_ROUTE FALSE [get_nets CP]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN U18} [get_ports CP]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN U16} [get_ports {D[0]}]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN R15} [get_ports {D[1]}]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN V15} [get_ports {D[2]}]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN T14} [get_ports {D[3]}]

set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN U6} [get_ports {Q[3]}]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN R5} [get_ports {Q[2]}]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN U7} [get_ports {Q[1]}]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN R6} [get_ports {Q[0]}]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN R7} [get_ports Max_Min]
set_property -dict {IOSTANDARD LVCMOS18 PACKAGE_PIN U8} [get_ports RCO_]