超前進位加法器

1、說明文檔4到8 LED編碼器4位超前進位加法器abcincout8段LED顯示器8段LED顯示器1.結(jié)構(gòu)圖：2.八段LED顯示器的編碼：假設8段LED顯示器是共陰極的，DPGFEDCBA正好組成一個8位的數(shù)8seg，給這個數(shù)賦值，即可以顯示相應的數(shù)字。編碼：3.編碼器子模塊4到8位LED編碼器module coder(in,out);input3:0 in;output7:0 out;wire3:0 in;reg7:0 out;always(in)begincase(in)4'h0: out=8'h3f;4'h1: out=8'h06;4'h2: out

2、=8'h5b;4'h3: out=8'h4f;4'h4: out=8'h66;4'h5: out=8'h6d;4'h6: out=8'h7d;4'h7: out=8'h07;4'h8: out=8'h7f;4'h9: out=8'h6f;4'ha: out=8'h77;4'hb: out=8'h7c;4'hc: out=8'h39;4'hd: out=8'h5e;4'he: out=8'h79;4

3、'hf: out=8'h71;endcaseendendmodule4. 超前進位加法器子模塊對一個4位全加器，第i位的兩加數(shù)分別是Ai和Bi,進位輸入信號是Ci-1,這個位產(chǎn)生的進位輸出是 Ci，則可以有得到：Ci=AiBi（AiBi）Ci-1令Gi= AiBi(進位產(chǎn)生函數(shù)) Pi= AiBi(進位傳遞函數(shù))則：Ci=Gi+ PiCi-1所以有：C0=G0+P0C-1 C1=G1+P1C0 C2=G2+P2C1 C3=G3+P3C2將上式逐次代入則可以得到如下表達式（C-1是最低位的進位輸入）COG0+P0C-1C1=G1+P1C0=G1+P1G0+P1P0C-1C2=G2

4、+P2C1=G2+P2G1+P2P1C0=G2+P2G1+P2P1G0+P2P1P0C-1C3=G3+P3C2 =G3+P3G2+P3P2C1 =G3+P3P2P3P2C1 =G3+P3P2P3P2G1P3P2P1C0 =G3+P3P2P3P2G1P3P2P1G0P3P2P1P0C-1上述表達式說明只要各位數(shù)據(jù)和最低位進位同時輸入，各位之間的進位信號與和就能同時產(chǎn)生。要據(jù)這樣的原理可以實現(xiàn)超前進位加法器，這種加法器運算速度顯著提高，但是復雜度也提高了。module add4_head( a, b, cin, sum,cout);input3:0 a;input3:0 b;input cin;

5、output3:0 sum;output cout;wire3:0 p;wire3:0 g;wire3:0 t;wire2:0 c;assign p0 = a0 | b0;assign p1 = a1 | b1;assign p2 = a2 | b2;assign p3 = a3 | b3;assign t0 = a0 b0;assign t1 = a1 b1;assign t2 = a2 b2;assign t3 = a3 b3;assign g0 = a0 & b0;assign g1 = a1 & b1;assign g2 = a2 & b2;assign g3

6、= a3 & b3;assign c0 = (p0 & cin) | g0;assign c1 = (p1 & c0) | g1;assign c2 = (p2 & c1) | g2;assign cout = g3 | (p3 & (g2 | p2 & (g1 | p1 & (g0|(p0&cin);assign sum0 = t0 cin;assign sum1 = t1 c0;assign sum2 = t2 c1;assign sum3 = t3 c2; endmodule5.例化兩個子模塊把超前進位加法器和4到8位LED

7、編碼器 兩個模塊例化放一起，完成本設計module add_display(a,b,cin,cout,out);input3:0 a;input3:0 b;input cin;output cout;output7:0 out;wire3:0 temp;add4_head add4_head(.a(a), .b(b), .cin(cin), .sum(temp), .cout(cout) );coder coder ( .in(temp), .out(out);endmodule6.對本設計進行測試/timescale 1ns / 1psmodule testbench;/ Inputsreg

8、 3:0 a;reg 3:0 b;reg cin;/ Outputswire 7:0 out;wire cout; add_display add_display(.a(a),.b(b),.cin(cin),.cout(cout),.out(out);integer m,n,l;initial begin a = 4'b0000; b = 4'b0000;cin= 0;/ Add stimulus herefor(m=0;m<2;m=m+1) for(n=0;n<16;n=n+1) for(l=0;l<16;l=l+1) begin a=n; b=l; cin

9、=m; #20; end end endmodule module fanlongfei5test;/ Inputsreg 3:0 a;reg 3:0 b;reg cin;/ Outputswire 7:0 out;wire cout;fanlongfeichao uut(.a(a),.b(b),.cin(cin),.cout(cout),.out(out);initial begin a=4'b0000;b=4'b0000;cin=0;#20a=4'b0000;b=4'b0000;cin=1;#20a=4'b0001;b=4'b0000;cin

10、=1;#20a=4'b0001;b=4'b0001;cin=1;#20a=4'b0100;b=4'b0100;cin=1;#20a=4'b1111;b=4'b0001;cin=1;#20a=4'b0001;b=4'b0000;cin=0;#20a=4'b0001;b=4'b0001;cin=0;#20a=4'b0100;b=4'b0100;cin=0;#20a=4'b1111;b=4'b0001;cin=0;#20;endendmodule4'b0000:out0=1000000;4'b0001:out0=1111001; 4'b0010:out0=0100100; 4'b0011:out0=011