【Verilog】HDLBits题解——Circuits/Combinational Logic

Combinational Logic

Basic Gates

• Wire

  题目链接

module top_module (
    input in,
    output out);
	assign out = in;
endmodule

• GND

  题目链接

module top_module (
    output out);
	assign out = 0;
endmodule

• NOR

  题目链接

module top_module (
    input in1,
    input in2,
    output out);
    assign out = ~(in1 | in2);
endmodule

• Another gate

  题目链接

module top_module (
    input in1,
    input in2,
    output out);
	assign out = in1 & ~in2;
endmodule

• Two gates

  题目链接

module top_module (
    input in1,
    input in2,
    input in3,
    output out);
    wire in1_in2 = in1 ^ in2;
	assign out = in3 ^ ~in1_in2;
endmodule

• More Logic Gates

  题目链接

module top_module( 
    input a, b,
    output out_and,
    output out_or,
    output out_xor,
    output out_nand,
    output out_nor,
    output out_xnor,
    output out_anotb
);
	assign out_and = a & b;
    assign out_or = a | b;
    assign out_xor = a ^ b;
    assign out_nand = ~(a & b);
    assign out_nor = ~(a | b);
    assign out_xnor = ~(a ^ b);
    assign out_anotb = a & ~b;
endmodule

• 7420 Chip

  题目链接

module top_module ( 
    input p1a, p1b, p1c, p1d,
    output p1y,
    input p2a, p2b, p2c, p2d,
    output p2y );
    assign p1y = ~((p1a & p1b) & (p1c & p1d));
    assign p2y = ~((p2a & p2b) & (p2c & p2d));
endmodule

• Truth Tables

  题目链接

module top_module( 
    input x3,
    input x2,
    input x1,  // three inputs
    output f   // one output
);
    assign f = (~x3 & x2) | (x3 & x1);
endmodule

• Two bits equality

  题目链接

module top_module ( input [1:0] A, input [1:0] B, output z ); 
    assign z = ~ (| (A ^ B));
endmodule

• Simple Circuit A

  题目链接

module top_module (input x, input y, output z);
    assign z = (x ^ y) & x;
endmodule

• Simple Circuit B

  题目链接

module top_module ( input x, input y, output z );
    assign z = ~(x ^ y);
endmodule

• Combine Circuits A and B

  题目链接

module top_module (input x, input y, output z);
	wire A_out = x & ~y;
    wire B_out = ~(x ^ y);
    assign z = (A_out | B_out) ^ (A_out & B_out);
endmodule

• Ring or Vibrate?

  题目链接

module top_module (
    input ring,
    input vibrate_mode,
    output ringer,       // Make sound
    output motor         // Vibrate
);
    assign {ringer, motor} = ring ? (vibrate_mode ? 2'b01 : 2'b10) : 2'b00;
endmodule

• Thermostat

  题目链接

module top_module (
    input too_cold,
    input too_hot,
    input mode,
    input fan_on,
    output heater,
    output aircon,
    output fan
); 
    assign heater = (mode & too_cold);
    assign aircon = (~mode & too_hot);
    assign fan = fan_on | (heater | aircon);
endmodule

• 3-bit population count

  题目链接

module top_module( 
    input [2:0] in,
    output [1:0] out );
    assign out[1] = (in[1] & in[0]) | (in[2] & in[1]) | (in[2] & in[0]);
    assign out[0] = (in[2] ^ in[1] ^ in[0]);
endmodule

• Gates and Vectors

  题目链接

module top_module( 
    input [3:0] in,
    output [2:0] out_both,
    output [3:1] out_any,
    output [3:0] out_different );
    assign out_both[2:0] = {in[3] & in[2], in[2] & in[1], in[1] & in[0]};
    assign out_any[3:1] = {in[3] | in[2], in[2] | in[1], in[1] | in[0]};
    assign out_different[3:0] = {in[0] ^ in[3], in[3] ^ in[2], in[2] ^ in[1], in[1] ^ in[0]};
endmodule

• Even longer vectors

  题目链接

module top_module( 
    input [99:0] in,
    output [98:0] out_both,
    output [99:1] out_any,
    output [99:0] out_different );
    assign out_both[98:0] = in[99:1] & in[98:0];//   {in[3] & in[2], in[2] & in[1], in[1] & in[0]};
    assign out_any[99:1] =  in[99:1] | in[98:0];//   {in[3] | in[2], in[2] | in[1], in[1] | in[0]};
    assign out_different[99:0] = {in[0], in[99:1]} ^ in[99:0];//{in[0] ^ in[3], in[3] ^ in[2], in[2] ^ in[1], in[1] ^ in[0]};
endmodule

Multiplexers

• 2-to-1 multiplexer

  题目链接

module top_module( 
    input a, b, sel,
    output out ); 
    assign out = sel ? b : a;
endmodule

• 2-to-1 bus multiplexer

  题目链接

module top_module( 
    input [99:0] a, b,
    input sel,
    output [99:0] out );
	assign out = sel ? b : a;
endmodule

• 9-to-1 multiplexer

  题目链接

module top_module( 
    input [15:0] a, b, c, d, e, f, g, h, i,
    input [3:0] sel,
    output [15:0] out );
    reg [15:0] out_reg;
    assign out = out_reg;
    always @ (*) begin
        case(sel) 
        	0: out_reg = a;
        	1: out_reg = b;
        	2: out_reg = c;
        	3: out_reg = d;
        	4: out_reg = e;
        	5: out_reg = f;
        	6: out_reg = g;
        	7: out_reg = h;
        	8: out_reg = i;
            default: out_reg = {16{1'b1}};
    	endcase
    end
endmodule

• 256-to-1 multiplexer

  题目链接

module top_module( 
    input [255:0] in,
    input [7:0] sel,
    output out );
    assign out = in[sel];
endmodule

• 256-to-1 4-bit multiplexer

  题目链接

module top_module( 
    input [1023:0] in,
    input [7:0] sel,
    output [3:0] out );
    assign out = {in[4 * sel + 3], in[4 * sel + 2], in[4 * sel + 1], in[4 * sel]};
endmodule

Arithmetic Circuits

• Half adder

  题目链接

module top_module( 
    input a, b,
    output cout, sum );
	assign cout = a & b;
    assign sum = a ^ b;
endmodule

• Full adder

  题目链接

module top_module( 
    input a, b, cin,
    output cout, sum );
	assign sum = a ^ b ^ cin;
    assign cout = (a & b) | (a & cin) | (b & cin);
endmodule

• 3-bit binary adder

  题目链接

module top_module( 
    input [2:0] a, b,
    input cin,
    output [2:0] cout,
    output [2:0] sum );
	
    genvar i;
    generate
        for (i = 0; i < 3; i = i + 1) begin : faddr_for
            if (i == 0) begin : faddr_for_0
                assign sum[i] = a[i] ^ b[i] ^ cin;
                assign cout[i] = (a[i] & b[i]) | (a[i] & cin) | (b[i] & cin);
            end
            else begin : faddr_for_else
                assign sum[i] = a[i] ^ b[i] ^ cout[i - 1];
                assign cout[i] = (a[i] & b[i]) | (a[i] & cout[i - 1]) | (b[i] & cout[i - 1]);
            end
        end
    endgenerate
endmodule

• Adder

  题目链接

module top_module (
    input [3:0] x,
    input [3:0] y, 
    output [4:0] sum);
    wire [3:0] cout;
    genvar i;
    assign sum[4] = cout[3];
    generate 
        for (i = 0; i < 4; i = i + 1) begin : generate_fadd_for
            if (i == 0) begin : fadd_0
                assign sum[i] = x[i] ^ y[i];
                assign cout[i] = x[i] & y[i];
            end
            else begin : fadd_else
                assign sum[i] = x[i] ^ y[i] ^ cout[i - 1];
                assign cout[i] = (x[i] & y[i]) | (x[i] & cout[i - 1]) | (cout[i - 1] & y[i]);
            end
        end
    endgenerate
endmodule

• Signed addition overflow

  题目链接

module top_module (
    input [7:0] a,
    input [7:0] b,
    output [7:0] s,
    output overflow
); //
 
    // assign s = ...
    // assign overflow = ...
    assign s = {a + b};
    assign overflow = (~a[7] & ~b[7] & s[7]) | (a[7] & b[7] & ~s[7]);
endmodule

• 100-bit binary adder

  题目链接

module top_module( 
    input [99:0] a, b,
    input cin,
    output cout,
    output [99:0] sum );
    assign {cout,sum} = (a + b + cin);
endmodule

• 4-digit BCD adder

  题目链接

module top_module ( 
    input [15:0] a, b,
    input cin,
    output cout,
    output [15:0] sum );
    wire [2:0] cout_tmp;
    wire [3:0] cin_wire;
    assign cin_wire = {cout_tmp,cin};
    wire [3:0] cout_wire;
    assign {cout,cout_tmp} = cout_wire;
    genvar i;
    generate
        for (i = 0; i < 4; i = i + 1) begin : generate_bcd_fadd_for
            bcd_fadd bcd_fadd_inst (
                .a(a[4 * i + 3 : 4 * i]),
                .b(b[4 * i + 3 : 4 * i]),
                .cin(cin_wire[i]),
                .cout(cout_wire[i]),
                .sum(sum[4 * i + 3 : 4 * i]));
        end
    endgenerate
endmodule

Karnaugh Map to Circuit

• 3-varible

  题目链接

module top_module(
    input a,
    input b,
    input c,
    output out  ); 
    assign out = a | b | c;
endmodule

• 4-varible

  题目链接

module top_module(
    input a,
    input b,
    input c,
    input d,
    output out  ); 
	reg out_reg;
    assign out = out_reg;
    always @ (*) begin
        case({a,b,c,d})
            'b1100: out_reg = 0;
            'b1101: out_reg = 0;
            'b0101: out_reg = 0;
            'b0011: out_reg = 0;
            'b1110: out_reg = 0;
            'b1010: out_reg = 0;
            default: out_reg = 1;
        endcase
    end
endmodule

• 4-varible

  题目链接

module top_module(
    input a,
    input b,
    input c,
    input d,
    output out  ); 
    assign out = a | (~b & c);
endmodule

• 4-varible

  题目链接

module top_module(
    input a,
    input b,
    input c,
    input d,
    output out  ); 
	assign out = a ^ b ^ c ^ d;
endmodule

• Minimum SOP and POS

  题目链接

module top_module (
    input a,
    input b,
    input c,
    input d,
    output out_sop,
    output out_pos
); 
    assign out_sop = (c & d) | (~a & ~b & c);
    assign out_pos = c & (~a | b) & (~c | d | ~b);
endmodule

• Karnaugh map

  题目链接

module top_module (
    input [4:1] x, 
    output f );
    assign f = (x[1] | x[3]) & (~x[1] | ~x[3]) & (x[2] | x[3]);
endmodule

• Karnaugh map

  题目链接

module top_module (
    input [4:1] x,
    output f
); 
    assign f = (~x[2] & ~x[4]) | (~x[1] & x[3]) | (x[2] & x[3] & x[4]);
endmodule

• K-map implemented with a multiplexer

  题目链接

module top_module (
    input c,
    input d,
    output [3:0] mux_in
); 
    assign mux_in = {c & d, ~d, 1'b0, c | d};
endmodule

* ### [题目链接]() ```clike s ```