可逆计数器设计实验
实验要求
![image-20211209195522061](https://cdn.jsdelivr.net/gh/Chaos-xBug/img/blog/202112091955965.png)
实验步骤
![image-20211209195629312](https://cdn.jsdelivr.net/gh/Chaos-xBug/img/blog/202112091956956.png)
74LS191模块代码
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| `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
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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
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| 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_]
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在实际实验中,可能会出现,在操作者“自认为的一个周期”(按一下CP
按键)内,计数器+/-
的值为2,甚至可能是3,这些可能是由于按键抖动造成的(按键消抖还没学,流下了菜菜的泪水)。